Hybrid vehicle and method of controlling hybrid vehicle

ABSTRACT

In a hybrid vehicle of the present invention, an engine EG is subjected to feedback control to attain a target revolving speed NE*. In the case of malfunction of an inverter P 1  for a generator GN, operation of the inverter P 1  is stopped. When the generator GN is driven to rotate at a predetermined rotational speed, a counter electromotive force arises in a multiphase phase coil of the generator GN. When a motor MG is connected to the generator GN as a loading, electric current runs via a protection diode of the inverter P 1  to implement power generation by the generator GN. The electric power generated by the generator GN is directly consumed by the motor MG. This arrangement enables the quantity of power generation to balance the quantity of consumption. Here the revolving speed of the engine EG is varied according to the loading applied to the vehicle. The arrangement of the present invention thus enables the amount of electric power generated by one of the generator GN and the motor MG to balance the amount of electric power consumed by the other of the generator GN and the motor MG, thus attaining a drive of the hybrid vehicle without using a secondary battery.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a hybrid vehicle and a method ofcontrolling the hybrid vehicle. More specifically the invention pertainsto a hybrid vehicle with an engine that outputs power through combustionof a fuel, a generator that generates electric power with at least partof the power output from the engine, and a motor that outputs power to adrive shaft of the vehicle, as well as a method of controlling such ahybrid vehicle.

[0003] 2. Description of the Related Art

[0004] A diversity of hybrid vehicles have been proposed. The hybridvehicle has a motor that outputs electric power as a driving force, inaddition to an engine that outputs power through combustion of a fuel,such as gasoline. The hybrid vehicle uses the engine as the final energysource and thus requires only the supply of gasoline or another fuel. Itis accordingly not required to socially provide new facilities andequipment, for example, power stations for charging batteries.

[0005] The hybrid vehicles are mainly classified into series hybridvehicles and parallel hybrid vehicles. The series hybrid vehicle usesall the power output from the engine to drive a generator, accumulatesthe electric power generated by the generator in a battery, and obtainsthe required driving force to be output to the drive shaft from a motor,which is driven with the electric power accumulated in the battery. Theparallel hybrid vehicle has a three shaft-type power distributingmechanism or a pair-rotor motor to distribute the power of the engine,for example, a gasoline engine, and causes the power output from theengine to supply part of the driving force to be output to the driveshaft. In the parallel hybrid vehicle, the residual power that is notoutput to the drive shaft is used for power generation by the generator.The generated electric power is generally accumulated in a battery or ahigh-capacity capacitor.

[0006] The electric power accumulated in the secondary battery or thehigh-capacity capacitor is used to drive the vehicle while the engine isat a stop. When the engine is driven but the driving force of the enginedoes not satisfy all the required torque, the motor utilizes theaccumulated electric power to supplement the insufficient torque.

[0007] In the hybrid vehicle of the above structure, in the case ofmalfunction of the secondary battery or the high-capacity capacitor thataccumulates the electric power therein or in the case of malfunction ofa charging circuit for charging the secondary battery or thehigh-capacity capacitor, operation of the generator is not allowed. Thismakes a further drive of the vehicle difficult. According to theprinciples of the hybrid vehicle, the vehicle can be driven by directlyconnecting the generator with the motor and driving the motor with thegenerated electric power. The drive mode in this state is called thebattery-less drive mode. In the case where the vehicle is actuallydriven in the direct connection of the generator with the motor,however, expected abrupt variations in loading on the motor during adrive cause a diversity of problems and troubles. There is a possibilitythat the loading or the required power of the drive shaft during a driveabruptly decreases within a very short time, due to racing of wheels orany braking operation. In such cases, the electric current to be flowninto the motor also abruptly decreases within a very short time. Theabrupt decrease in required electric current causes a high impedance inthe generator that is driven in stationary state by the engine. Thisabruptly raises the voltage between terminals of the generator andcauses an unexpectedly high voltage to be applied to the circuit andexceed the rated power of the circuit.

[0008] In the actual state, these problems make the battery-less drivemode substantially unpractical. It is difficult to actualize the limphome capability that enables the vehicle to be anyway driven to a gasstation while the battery or its charging circuit malfunctions.Especially in the case of malfunction of a switching element included inan inverter that is connected to the generator to form the chargingcircuit, even when the engine, the generator, and the motor are allnormally operable, the vehicle is driven only with the electric poweraccumulated in the battery. This undesirably leads to a restricteddriving distance or a limited vehicle speed.

[0009] The secondary battery used in the hybrid vehicle is a highvoltage battery. Positive and negative power lines respectively havecontacts to cut off the connection of the power lines with the secondarybattery in the inactive state. These contacts are kept open when thevehicle is not used or when some abnormality is detected in the battery.The open position of the contacts prevents the high voltage of thesecondary battery from being applied to the power lines when notrequired. These contacts are used to allow and forbid a large flow ofelectric current and are thereby often subject to troubles like welding.The prior art arrangement accordingly connects the power line with astandard contact in parallel via a resistor for restricting the electriccurrent and an auxiliary contact. The procedure first closes theauxiliary contact to allow a restricted flow of electric current andthen closes the standard contact.

[0010] In this prior art arrangement, however, there is still apossibility that the contact welds. In response to detection of a weldof the contact in either one of the positive and negative power lines,the prior art arrangement prohibits the use of the secondary battery. Ifthe continuous use of the secondary battery is allowed in the weldingstate of one contact, the connection of the secondary battery with thepower lines can not be cut off in case of a weld of the other contact.

SUMMARY OF THE INVENTION

[0011] The object of the present invention is thus to attain a drive ofa hybrid vehicle with an engine, a generator, and a motor mountedthereon without using a secondary battery.

[0012] At least part of the above and the other related objects isactualized by a first hybrid vehicle with an engine, a generator, and amotor mounted thereon, wherein the engine outputs power throughcombustion of a fuel, the generator provided with permanent magnetsgenerates electric power with at least part of the power output from theengine, and the motor outputs power to a drive shaft of the hybridvehicle. The first hybrid vehicle includes: an engine control unit thatfeedback controls a quantity of the fuel injected to the engine toattain a specified target revolving speed of the engine; a powergeneration control unit that causes the generator to carry out powergeneration utilizing a counter electromotive force; a loading detectionunit that specifies a loading applied to the hybrid vehicle; a generatorrotational speed variation unit that varies a rotational speed of thegenerator, based on the specified loading; and a motor driving unit thatdrives the motor with the electric power generated by the generator atthe varying rotational speed.

[0013] There is also a method of controlling the hybrid vehicle, whichcorresponds to the arrangement of the first hybrid vehicle. The presentinvention is accordingly directed to a first method of controlling ahybrid vehicle, wherein an engine outputs power through combustion of afuel, a generator provided with permanent magnets generate electricpower with at least part of the power output from the engine, and amotor is driven with at least part of the electric power generated bythe generator, so as to output power to a drive shaft of the vehicle.The first method includes the steps of: feedback controlling a quantityof the fuel injected to the engine to attain a specified targetrevolving speed of the engine; causing the generator to carry out powergeneration utilizing a counter electromotive force; specifying a loadingapplied to the hybrid vehicle; varying a rotational speed of thegenerator, based on the specified loading; and driving the motor withthe electric power generated by the generator at the varying rotationalspeed.

[0014] The first hybrid vehicle of the present invention or thecorresponding first method of controlling the hybrid vehicle feedbackcontrols the quantity of the fuel injected to the engine, in order tomake the actual revolving speed of the engine coincident with aspecified target revolving speed. This arrangement effectively preventsthe revolving speed of the engine from varying with a variation inloading of the generator, which generates electric power with at leastpart of the power output from the engine. While the generator carriesout power generation utilizing a counter electromotive force, the motorconsumes the electric power generated by the generator and carries outthe power operation. The rotational speed of the generator is variedaccording to the loading applied to the vehicle. This arrangementenables the adequate power corresponding to the loading of the vehicleto be output to the drive shaft of the vehicle. The arrangement ofvarying the rotational speed of the generator with a variation inloading applied to the vehicle effectively prevents the rotational speedof the generator from being unnecessarily heightened under the conditionof low loading.

[0015] In accordance with one preferable application of the presentinvention, the hybrid vehicle further includes: an inverter thatswitches electric current running through a multiphase coil of thegenerator; and a secondary battery that is charged with the directcurrent converted by the switching operation of the inverter. Thecontrol procedure causes the power generation control unit, thegenerator rotational speed variation unit, and the motor driving unit toimplement their functions, in response to detection of an abnormalstate, which does not allow the secondary battery to be charged via theinverter. The power generation utilizing the counter electromotive forcehas stricter restrictions, for example, on the maximum power generation,compared with the power generation utilizing the inverter. The powergeneration utilizing the counter electromotive force is accordinglycarried out in the state that does not allow the secondary battery to becharged via the inverter.

[0016] In the hybrid vehicle of the above application, when an observedvoltage level of the secondary battery is higher than the counterelectromotive force utilized for the power generation via the powergeneration control unit, one preferable arrangement prohibits the powergeneration utilizing the counter electromotive force via the powergeneration control unit but drives the motor with electric poweraccumulated in the secondary battery. In the case where the secondarybattery has a sufficiently high voltage level as its state of charge,the motor may be driven with the electric power taken out of thesecondary battery. During a drive of the hybrid vehicle, the secondarybattery may be charged with the regenerative electric power. In suchcases, the hybrid vehicle advantageously uses engine brake.

[0017] In the first hybrid vehicle of the present invention, the targetrevolving speed of the engine may be specified, based on behavior of anaccelerator pedal. The behavior of the accelerator pedal is highlycorrelated to the power requirement of the vehicle expected in the nearfuture. For example, depression of the accelerator pedal leads to anincrease in required power to be output to the drive shaft. Thearrangement of specifying the target revolving speed of the engine bytaking into account such correlation enables the upper limit of energyoutput from the engine to be adjusted at an earlier timing. Onepreferable procedure increases the rotational speed of the generatorwith an increase in amount of depression of the accelerator pedal. Thequick response to the increase in amount of depression of theaccelerator pedal significantly improves the drivability.

[0018] In accordance with another preferable application of the presentinvention, the target revolving speed of the engine is lowered or raisedin response to detection of an increasing tendency or a decreasingtendency of an actual revolving speed of the engine relative to thetarget revolving speed of the engine. The engine is under the feedbackcontrol to attain the target revolving speed. Controlling the drivingstate of the generator instantaneously increases or decreases the actualrevolving speed of the engine. The control procedure of this applicationlowers or increases the target revolving speed of the engine in responseto a variation in actual revolving speed of the engine. This anticipatesa variation in loading in the near future. Such control is especiallyeffective when separate control units are in charge of control of theengine and control of the generator and the motor and there is someinterference with transmission of the target revolving speed between theseparate control units, for example, via communication. The controlprocedure of this application may, however, be adopted in otherstructures that do not require transmission of the target revolvingspeed in such manner.

[0019] In the hybrid vehicle of the above application, one preferablecontrol procedure urges the power generation utilizing the counterelectromotive force, when an external force makes the drive shaftinversely rotated and the motor fall into a state of power generation.When there is an insufficiency of torque output from the vehicle, forexample, running on a steep ascent, the vehicle may go back. In suchcases, the drive shaft is inversely rotated and the motor falls into thestate of power generation. The above control procedure desirablyprevents over-voltage in such cases.

[0020] In the first hybrid vehicle of the present invention, onepreferable control procedure sets a maximum electric power generated bythe generator with the power of the engine, specifies driving electricpower consumed for driving the motor within the preset maximum electricpower, based on the specified loading. The control procedure drives thegenerator to generate electric power that is equivalent to the drivingelectric power consumed by the motor, and regulates the electric currentrunning through a multiphase coil of the motor with the generatedelectric power. The control procedure of this application sets themaximum electric power generated by the generator and ensures thebalance of the generated electric power with the consumed electric powerwithin the preset maximum electric power.

[0021] The present invention is also directed to a second hybrid vehiclewith an engine, a generator, and a motor mounted thereon, wherein theengine outputs power through combustion of a fuel, the generatorgenerates electric power with at least part of the power output from theengine, and the motor outputs power to a drive shaft of the hybridvehicle. The second hybrid vehicle includes: an engine control unit thatfeedback controls a quantity of the fuel injected to the engine toattain a specified target revolving speed of the engine; a generativeenergy computation unit that computes an instantaneous magnitude ofgenerative energy to be generated by the generator by taking intoaccount an energy balance in a system including the engine, thegenerator, and the motor; a voltage measurement unit that measures agenerative voltage of the generator; a control variable computation unitthat computes a feedback control variable corresponding to a differencebetween the observed generative voltage and a target generative voltageof the generator; a generator control unit that feedback controls thegenerator with the calculated instantaneous magnitude of generativeenergy and the calculated feedback control variable; a requirementdetection unit that detects a requirement on a drive of the vehicle; anda motor driving unit that calculates an output torque of the motor basedon a direct torque output from the generator, which is under control ofthe generator control unit, and a required torque related to thedetected requirement on the drive of the vehicle, and drives the motorto attain the calculated output torque.

[0022] There is also a method of controlling the hybrid vehicle, whichcorresponds to the arrangement of the second hybrid vehicle. The presentinvention is accordingly directed to a second method of controlling ahybrid vehicle, wherein an engine outputs power through combustion of afuel, a generator provided with permanent magnets generate electricpower with at least part of the power output from the engine, and amotor is driven with at least part of the electric power generated bythe generator, so as to output power to a drive shaft of the vehicle.The second method includes the steps of: feedback controlling a quantityof the fuel injected to the engine to attain a specified targetrevolving speed of the engine; computing an instantaneous magnitude ofgenerative energy to be generated by the generator by taking intoaccount an energy balance in a system including the engine, thegenerator, and the motor; measuring a generative voltage of thegenerator; computing a feedback control variable corresponding to adifference between the observed generative voltage and a targetgenerative voltage of the generator; feedback controlling the generatorwith the calculated instantaneous magnitude of generative energy and thecalculated feedback control variable; detecting a requirement on a driveof the vehicle; and calculating an output torque of the motor based on adirect torque output from the generator, which is under control of thegenerator control unit, and a required torque related to the detectedrequirement on the drive of the vehicle, and driving the motor to attainthe calculated output torque.

[0023] The second hybrid vehicle of the present invention or thecorresponding second method of controlling the hybrid vehicle carriesout the control according to the calculated instantaneous magnitude ofgenerative energy to be generated by the generator as well as accordingto the calculated feedback control variable. The instantaneous magnitudeof generative energy is calculated by taking into account the energybalance in the system including the engine, the generator, and themotor. The feedback control variable is calculated corresponds to thedifference between the observed generative voltage of the generator anda target generative voltage. Even when the generative voltage of thegenerator varies with a variation in loading, this arrangement ensuresthe quick response to such a variation and makes the quantity of energygeneration balance with the quantity of energy consumption. This enablesthe hybrid vehicle to be driven without charging or discharging thesecondary battery.

[0024] In accordance with one preferable application of the presentinvention, the generator uses permanent magnets to form a magneticfield, and the hybrid vehicle further includes: an inverter thatswitches electric current running through a multiphase coil of thegenerator; a secondary battery that is charged with the direct currentconverted by the switching operation of the inverter. The controlprocedure stops the switching operation of the inverter and causes thegenerator to carry out power generation utilizing a counterelectromotive force, in response to detection of a state of failure infeedback control of the generator using the feedback control variable.In the case where the feedback control of the generator falls into thestate of failure, this arrangement quickly stops this feedback controland causes the generator to carry out power generation utilizing thecounter electromotive force. This arrangement effectively prevents thefailure of the whole control. Although there is the upper limit, thepower generation utilizing the counter electromotive force enables thepower generation according to the quantity of power consumption andthereby makes the quantity of energy generation balance with thequantity of energy consumption. In the case where the feedback controlof the generator through the switching operation of the inverter fallsinto the state of failure due to some disturbance, the temporary shiftto the power generation utilizing the counter electromotive forceeffectively recovers the total state of control.

[0025] In the second hybrid vehicle of the present invention, in aspecific driving state where the motor generates electric power, forexample, in the course of braking, one preferable control procedurestops the fuel injection to the engine and causes the generator to motorthe engine and thereby consume the electric power generated by themotor. This arrangement enables the hybrid vehicle to use engine brake.

[0026] The present invention is also directed to a third hybrid vehiclewith an engine, a generator, and a motor mounted thereon, wherein theengine outputs power through combustion of a fuel, the generatorgenerates electric power with at least part of the power output from theengine, and the motor outputs power to a drive shaft of the hybridvehicle. The third hybrid vehicle includes: an engine control unit thatfeedback controls a quantity of the fuel injected to the engine toattain a specified target revolving speed of the engine; a secondarybattery that is connectable with both positive and negative power linesof a direct voltage source, which link the generator with the motor; afirst contact that switches on and off connection of the secondarybattery with one of the two power lines and links the secondary batterywith the power line via a restriction resistor, which restricts electriccurrent flowing out of the secondary battery; a second contact that isconnected to the first contact in parallel and directly links thesecondary battery with the power line; a third contact that switches onand off connection of the secondary battery with the other of the twopower lines; a weld detection unit that detects a weld of the thirdcontact; and a welding-state driving unit that opens both the firstcontact and the second contact after activation of the engine inresponse to detection of the weld of the third contact, and drives themotor with the electric power generated by the generator.

[0027] There is also a method of controlling the hybrid vehicle, whichcorresponds to the arrangement of the third hybrid vehicle. The presentinvention is accordingly directed to a third method of controlling ahybrid vehicle, wherein an engine outputs power through combustion of afuel, a generator provided with permanent magnets generate electricpower with at least part of the power output from the engine, and amotor is driven with at least part of the electric power generated bythe generator, so as to output power to a drive shaft of the vehicle.The third method includes the steps of: connecting a secondary batterywith both positive and negative power lines of a direct voltage source,which link the generator with the motor; interposing a first contactbetween the secondary battery and one of the two power lines via arestriction resistor, which restricts electric current flowing out ofthe secondary battery; connecting a second contact to the first contactin parallel, the second contact directly linking the secondary batterywith the power line: interposing a third contact between the secondarybattery and the other of the two power lines; feedback controlling aquantity of the fuel injected to the engine to attain a specified targetrevolving speed of the engine; detecting a weld of the third contact;and opening both the first contact and the second contact afteractivation of the engine in response to detection of the weld of thethird contact, and driving the motor with the electric power generatedby the generator.

[0028] In the third hybrid vehicle of the present invention or thecorresponding third method of controlling the hybrid vehicle, even whenthe third contact welds, once the engine is activated, the controlprocedure opens the first contact and the second contact and drives themotor with the electric power generated by the generator. Thisarrangement cuts off the connection of the power line with the secondarybattery and thus protects the first contact and the second contact fromwelding during a drive of the vehicle. There is no necessity that thedrive of the vehicle is prohibited, because of possible welding of thefirst contact and the second contact. This arrangement accordinglyenhances the convenience of the user while maintaining the sufficientsafety. The weld of the third contact is readily detected by setting apredetermined sequence to the on-off timings of the respective contactsand monitoring an inter-terminal voltage between terminals of thesecondary battery and an inter-power line voltage between the positiveand negative power lines of the direct voltage source.

[0029] In the third hybrid vehicle of the present invention, onepreferable control procedure measures both then inter-terminal voltagebetween the terminals of the secondary battery and the inter-power linevoltage between the two power lines and stops a drive of the vehiclewhen it is determined that the observed inter-terminal voltage is equalto the observed inter-power line voltage. This state suggests welding ofthe first contact or the second contact.

[0030] A diversity of structures are applicable to any of the firstthrough the third hybrid vehicles of the present invention and thehybrid vehicles in the corresponding first through the third methodsdiscussed above. Typical structures are a series hybrid vehicle and aparallel hybrid vehicle. In one preferable example, the generator has apair-rotor structure including a pair of rotors rotatable relative toeach other and carries out power generation to attain a voltage andelectric power corresponding to a sliding rotational speed of the tworotors. This structure corresponds to an electrical distribution typeparallel hybrid vehicle. There is also a mechanical distribution typeparallel hybrid vehicle. In this structure, the generator is linked withone shaft of a three-shaft power distributor, in which power input toand output from one shaft is automatically determined when powers inputto and output from residual two shafts are specified. One example of thethree-shaft power distributor is a planetary gear mechanism. Anothershaft of the three-shaft power distributor is linked with an outputshaft of the engine and still another shaft of the three-shaft powerdistributor is linked with the drive shaft of the vehicle. The parallelhybrid vehicle uses part of the power output from the engine as thedriving force of the drive shaft. This desirably reduces the size of themotor in the parallel hybrid vehicle.

[0031] In one applicable structure for any of the first through thethird hybrid vehicles and the corresponding first through third methods,the generator is connected to a first electric power driving circuitthat causes the generator to carry out either one of a generativeoperation and a power operation, based on an on-off state of switchingelements included in the first electric power driving circuit, and themotor is connected to a second electric power driving circuit thatcauses the motor to carry out either one of a power operation and agenerative operation, based on an on-off state of switching elementsincluded in the second electric power driving circuit. This correspondsto the structure of a semiconductor inverter and ensures accuratecontrol through regulation of the switching elements. Connection of thefirst electric power driving circuit with the second electric powerdriving circuit in this structure enables the hybrid vehicle to bedriven in a battery-less drive mode that is free from the connection ofthe battery. It is, however, also practical to have a battery drive modethat is under the connection of the battery. In the latter case, asecondary battery or a high-capacity capacitor is connected to at leastthe first electric power driving circuit. Such connection enables theelectric power generated by the generator to be accumulated in thesecondary battery or the high-capacity capacitor.

[0032] In the structure that allows the hybrid vehicle to be driven inthe battery-less drive mode, one preferable embodiment provides a cutoffunit that cuts off connection between the secondary battery and thefirst electric power driving circuit. At least when a generative voltageby the generator is higher than an inter-terminal voltage betweenterminals of the secondary battery, the cutoff unit is actuated to cutoff the connection between the secondary battery and the first electricpower driving circuit. In the battery-less drive mode, when thesecondary battery has a low voltage level, part of the generatedelectric power may be used to charge the secondary battery. This reducesthe amount of electric power used for driving. The arrangement ofcutting off the connection between the secondary battery and the firstelectric power driving circuit by means of the cutoff unit enables allthe generated electric power to be used for driving the motor.

[0033] In the hybrid vehicle of the above structure, in response todetection of a specific state that does not allow the secondary batteryto be charged via the first electric power driving circuit, onepreferable procedure drives the motor with electric current that isinduced by a counter electromotive force generated between terminals ofthe multiphase coil of the generator through the operation of the engineand runs via a rectifier arranged in combination with each switchingelement in the first electric power driving circuit. Even in the case ofmalfunction of the switching element in the first electric power drivingcircuit, this arrangement assures power generation by the generator. Inthis structure, the generated electric power is autonomously determinedaccording to the loading. This significantly facilitates the drive ofthe hybrid vehicle in the battery-less drive mode.

[0034] These and other objects, features, aspects, and advantages of thepresent invention will become more apparent from the following detaileddescription of the preferred embodiments with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035]FIG. 1 shows the configuration of a hybrid vehicle in oneapplication of the present invention;

[0036]FIG. 2 schematically illustrates the general structure of a hybridvehicle in one embodiment of the present invention;

[0037]FIG. 3 shows connection of driving circuits with motors MG1 andMG2 in the hybrid vehicle of FIG. 2;

[0038]FIG. 4A shows connection of an HV battery with system main relaysSMR1, SMR2, and SMR3 in the hybrid vehicle of FIG. 2;

[0039]FIG. 4B shows a time sequence of on and off of relays SMR1,SMR2,and SMR3;

[0040]FIG. 5 is a block diagram illustrating the general configurationof a control system in the hybrid vehicle;

[0041]FIG. 6 is a flowchart showing a failure detection-time controlroutine for battery-less drive executed in the embodiment;

[0042]FIG. 7 is a graph showing the target revolving speed NE* of anengine plotted against the vehicle speed SPD;

[0043]FIG. 8 is a graph showing an operation line OL in the mechanicaldistribution type hybrid vehicle;

[0044]FIG. 9 is a graph showing the counter electromotive force Vplotted against the revolving speed Ng of the motor MG1 to describe thestate of power generation utilizing the counter electromotive force;

[0045]FIG. 10 is a graph showing the amount of power generation P by themotor MG1 plotted against the revolving speed Ng of the motor MG1;

[0046]FIG. 11 shows a maximum generated output Pgmx at a predeterminedrevolving speed in the motor MG1;

[0047]FIG. 12 is a flowchart showing an essential part of a loadingcontrol routine executed by a master control CPU;

[0048]FIG. 13 shows a variation in motor torque Tm and a variation inrevolving speed NE of the engine;

[0049]FIG. 14 is a flowchart showing an essential part of a targetrevolving speed regulation routine executed by an engine ECU;

[0050]FIG. 15 is a flowchart showing a drive control routine forbatter-less drive using inverters;

[0051]FIG. 16 is a graph showing a loss in the motor MG1;

[0052]FIG. 17 is a graph showing the torque Tg plotted against therevolving speed Ng of the motor MG1 with regard to the voltage Vm as aparameter;

[0053]FIG. 18 is a graph showing the relationship between the maximumoutput torque Temx and the revolving speed Ne of the engine;

[0054]FIG. 19 is a graph showing the required torque Td plotted againstthe vehicle speed with regard to the depression amount AP of theaccelerator pedal as a parameter;

[0055]FIG. 20 is a flowchart showing a drive control routine in thestate of a welding failure of the system main relay SMR3;

[0056]FIG. 21 schematically illustrates the structure of a power outputsystem in an electrical distribution type hybrid vehicle; and

[0057]FIG. 22 shows a change of the drive mode in the hybrid vehicle.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] For the purpose of clarifying the configuration and the functionsof the present invention, one mode of carrying out the present inventionis discussed blow. FIG. 1 shows the configuration of a hybrid vehicle inone application of the present invention. An engine EG is an internalcombustion engine, in which gasoline is ejected from a fuel ejectionvalve IJ disposed in an intake port, taken into a cylinder SL by meansof the motion of a piston PT, compressed by the piston PT, and ignitedwith spark of a spark plug IP to be explosively combusted. The energy ofcombustion is taken out via the piston PT as rotating motions of acrankshaft CS. Driving conditions of the engine EG, especially theopening of a throttle valve TH and the quantity of fuel injection, areregulated by a specific engine control unit EFIECU. The engine controlunit EFIECU receives an observed revolving speed NE of the crankshaft CSmeasured by a speed sensor S1 and carries out feedback control with apredetermined gain G to make the observed revolving speed NE coincidentwith an externally given target revolving speed NE*.

[0059] A planetary gear unit PG is interposed between the crankshaft CSof the engine EG and a drive shaft DS of the vehicle. The planetary gearunit PG has three rotating shafts, which are respectively linked withthe crankshaft CS, a generator GN, and the drive shaft DS. A motor MG isalso disposed on the drive shaft DS. The torque transmitted from theengine EG via the planetary gear unit PG and the torque input into andoutput from the motor MG are transmitted to drive wheels via adifferential gear DF. A speed sensor S2 and a speed sensor S3 arerespectively attached to the generator GN and the drive shaft DS tomeasure the rotational speeds thereof.

[0060] Semiconductor inverters P1 and P2 are respectively connected tothe generator GN and the motor MG as driving circuits. Controlling theon-off state of switching elements in the inverters P1 and P2 regulatesthe generated electric power by the generator GN and the power outputfrom the motor MG. Power lines of these two inverters P1 and P2 aremutually linked with each other. A battery BT is connected to the powerlines via a system main relay SMR. While the vehicle runs in a normalstate, the system main relay SMR is kept ON (that is, in the state ofconnection), and the electric power generated by the generator GN isaccumulated in the battery BT. The motor MG is driven by consuming theelectric power accumulated in the battery BT. In this configuration, themotor MG may be used as a generator, and the generator GN may be used asa motor.

[0061] A system controller SCNT controls the inverters P1 and P2 and thesystem main relay SMR. The system controller SCNT connects with thespeed sensors S2 and S3, an accelerator pedal sensor APS that measuresthe amount of depression (the step-on amount) of an accelerator pedalAC, a remaining charge sensor RCS that measures a state of charge orremaining charge SOC of the battery BT, and the inverters P1 and P2. Thesystem controller SCNT outputs the target revolving speed NE* of theengine EG to the engine control unit EFIECU.

[0062] During a normal run, the system controller SCNT calculates thepower (revolving speed×torque) to be output to the drive shaft DS of thevehicle and the electric power to be generated by the generator GN,based on the observed amount of depression of the accelerator pedal AC,an observed revolving speed Nd of the drive shaft DS, and the observedstate of charge SOC of the battery BT. The system controller SCNT thencontrols the engine EG and the inverters P1 and P2 to attain the outputof the calculated power and the generation of the calculated electricpower. Whereas the engine control unit EFIECU controls the operations ofthe engine EG, the system controller SCNT outputs the target revolvingspeed NE* to indirectly regulate the output of the engine EG. Theprinciple of this regulation is described briefly.

[0063] The engine control unit EFIECU feedback controls the revolvingspeed of the engine EG. When there is a difference ΔN between the targetrevolving speed NE* and the actual revolving speed NE, the enginecontrol unit EFIECU regulates the quantity of air intake and thequantity of fuel injection and controls the power (revolvingspeed×torque) output from the engine EG, so as to make the actualrevolving speed NE coincident with the target revolving speed NE*. Inthe mechanical distribution type hybrid vehicle shown in FIG. 1, theplanetary gear unit PG is linked with the crankshaft CS. The generatorGN and the drive shaft DS are linked with the other shafts of theplanetary gear unit PG. The drive shaft DS is also connected to themotor MG. Controlling the generator GN and the motor MG forciblyregulates the revolving speed NE of the crankshaft CS. This arrangementenables the control that prevents the difference ΔN between the targetrevolving speed NE* and the actual revolving speed NE from beingimmediately reduced to zero even when the engine control unit EFIECUincreases the quantity of air intake and the quantity of fuel injection.When the difference ΔN is not reduced, the engine control unit EFIECUfurther regulates the quantity of air intake and the quantity of fuelinjection, so as to further increase or decrease the power possiblytaken out of the engine EG. The system controller SCNT specifies thetarget revolving speed NE* and regulates the rotational speeds of thegenerator GN and the motor MG. This regulates the revolving speed NE ofthe crankshaft CS and freely adjusts the energy taken out of the engineEG.

[0064] Based on the hardware structure and the principle of controldiscussed above, the system controller SCNT shown in FIG. 1 carries outthe following control procedure in response to the occurrence of afailure. The system controller SCNT first detects a failure arising, forexample, in the battery BT or the inverter P1 of the generator GN (stepSA), and sets the inverter P1 and the system main relay SMR OFF inresponse to detection of the failure (step SB). The switch-off operationdisconnects the battery BT from the circuit of the inverters P1 and P2.The system controller SCNT then reads the revolving speeds of therespective shafts (step SC) and measures the amount of depression AP ofthe accelerator pedal (step SD). The system controller SCNT subsequentlychanges the rotational speed of the generator GN according to therequired output of the vehicle calculated from the observed amount ofdepression AP and the resolving speed of the drive shaft DS (step SE),and controls the motor MG corresponding to the requirement of thevehicle (step SF).

[0065] In the state of the failure, the generator GN carries out powergeneration by utilizing the counter electromotive force of the generatorGN, instead of the general inverter-induced power generation. In thenormal state, the generator GN takes out the electric current induced byits coil, through which a magnetic field formed by permanent magnetspasses, thereby implementing the power generation. In the case ofmalfunction of the inverter P1, however, this general mechanism of powergeneration is not usable. Even when the inverter P1 is at a stop, themagnetic filed passing through the coil varies with the rotation of therotating shaft. A counter electromotive force is generated between bothends of the coil, in order to cancel the variation in magnetic field.When some load is connected to the power line, the counter electromotiveforce generated between both ends of the coil causes electric current tobe flown into the load via a protection diode arranged in combinationwith each switching element in the inverter P1. The generated output bythe generator GN in this state is determined autonomously according tothe magnitude of electric current flowing through the loading. Thegenerated output by utilizing the counter electromotive force isrestricted to be not greater than a predetermined value, whichcorresponds to a preset lower limit voltage, since the voltage decreaseswith an increase in output electric current. This predetermined value isspecified as a maximum generated power.

[0066] The above control procedure causes the vehicle to be driven inthe following manner. When the system controller SCNT reads a driver'srequirement from the amount of depression AP of the accelerator pedaland the revolving speed of the drive shaft DS and regulates the power(revolving speed×torque) output to the motor MG (step SF), the electricpower required by the motor MG is generated by utilizing the counterelectromotive force of the generator GN. The energy source of powergeneration by the generator GN is the engine EG. It is accordinglyrequired to control the output of the engine EG according to thevariation in generated electric power. This is attained by the feedbackcontrol of the revolving speed as discussed previously. The engine EG isunder the feedback control to the target revolving speed NE* by theengine control unit EFIECU. When the revolving speed NE of thecrankshaft CS is lowered, for example, due to an increase in generatedoutput by the generator GN or an increase in loading on the drive shaftDS of the vehicle, the engine control unit EFIECU increases the quantityof air intake and the quantity of fuel injection and raises the outputof the engine EG. At the same time, the rotational speed of thegenerator GN is varied according to the loading of the vehicle. Thegenerator GN is accordingly controlled with the engine EG as the energysource, in order to enable a greater power to be taken out correspondingto an increase in required power to be output to the drive shaft DS.

[0067] The above control procedure allows the continuous powergeneration by the generator GN and enables the vehicle to be driven withthe engine EG and the motor MG and safely reach a power station or anyequivalent facility even in the case of malfunction of the battery BT orthe inverter P1. The above description regards the limp home drive modein the case of a malfunction. The technique of the present invention is,however, not restricted to the control procedure in the state of afailure but is applicable to any battery-less drive mode. Some modes ofcarrying out the present invention are discussed below as preferredembodiments.

[0068] The hybrid vehicle in one embodiment of the present invention isdiscussed below in the following sequence:

[0069] A. General Structure of Hybrid Vehicle

[0070] B. Basic Operations in Hybrid Vehicle

[0071] C. Configuration of Control System in Embodiment

[0072] D. Control by Engine ECU

[0073] E. Other Configuration

[0074] F. Control Procedure in Response to Detection of Failure

[0075] G. Battery-less Drive in Normal State of Inverters

[0076] H. Control Procedure in State of Welding Failure of System MainRelay

[0077] I. Structure of Electrical Distribution Type

[0078] J. Change of Drive Mode

[0079] A. General Structure of Hybrid Vehicle

[0080]FIG. 2 schematically illustrates the general structure of a hybridvehicle in one embodiment of the present invention. The hybrid vehiclehas three prime movers, that is, one engine 150 and two motor generatorsMG1 and MG2. Here the motor generator represents the prime moverfunctioning as both a motor and a generator. In the descriptionhereinafter, for simplicity of explanation, the motor generators aresimply referred to as the motors. The hybrid vehicle is under thecontrol of a control system 200.

[0081] The control system 200 includes a main ECU 210, a brake ECU 220,a battery ECU 230, and an engine ECU 240. Each of these ECUs isconstructed as an integral unit, where a plurality of circuit elementsincluding a microcomputer, an input interface, and an output interfaceare arranged on one identical circuit board. The main ECU 210 includes amotor controller 260 and a master controller 270. The master controller270 functions to determine a variety of control-relating quantities, forexample, distribution of the output from the three prime movers 150,MG1, and MG2.

[0082] The engine 150 is an ordinary gasoline engine that explosivelycombusts gasoline as fuel and rotates a crankshaft 156 with thecombustion energy. The engine ECU 240 controls operations of the engine150. The engine ECU 240 drives a throttle motor 152 to regulate theopening θ of a throttle valve 151 disposed in an air intake pipe andactuates a fuel injection valve 154 to regulate the quantity of fuelinjection τ into the engine 150, based on the target revolving speed NE*directed by the master controller 270.

[0083] The motors MG1 and MG2 are constructed as synchronous motors, andrespectively include rotors 132 and 142 with a plurality of permanentmagnets mounted on outer circumferences thereof, and stators 133 and 143with three-phase coils 131 and 141 wound thereon to form revolvingmagnetic fields. The stators 133 and 142 are m fixed to a casing 119.The three-phase coils 131 and 141 wound on the stators 133 and 143 ofthe motors MG1, and MG2 are respectively connected to a secondarybattery or high voltage (HV) battery 194 via driving circuits 191 and192. FIG. 3 shows in detail the connection of the driving circuits 191and 192 with the motors MG1 and MG2. The driving circuits 191 and 192are constructed as transistor inverters that respectively includetransistors Tr1 through Tr6 and Tr11 through Tr16, which are arranged inpairs for the respective phases, between power lines L1 and L2 connectedto the HV battery 194 via a system main relay SMR. A capacitor C isinterposed between the power lines L1 and L2 to relieve a voltagevariation. A protection diode D is in inverse contact between acollector and an emitter of each of the switching elements Tr1 throughTr6 and Tr11 through Tr16.

[0084] The driving circuits 191 and 192 are controlled by the motorcontroller 260. The driving circuit 191 has current sensors 181 and 182that respectively measure the U-phase electric current and the V-phaseelectric current, whereas the driving circuit 192 has similar currentsensors 185 and 186. Observed values of electric current Iu1, Iv1, Iu2,and Iv2 are input into the motor controller 260. The motor controller260 receives the observed phase currents and outputs control signals Sw1and Sw2 to attain the desired power output. The transistors included inthe driving circuits 191 and 192 are switched on and off, in response tothe output control signals Sw1 and Sw2. The electric current flowsbetween the battery 194 and the motors MG1 and MG2 via the transistorsin the ON state. Each of the motors MG1 and MG2 may function as themotor that receives a supply of electric power from the HV battery 194to be driven and rotated (hereinafter this state of operation isreferred to as the power operation). While the rotor 132 or 142 isrotated by an external force, the motor MG1 or MG2 may function as thegenerator that causes an electromotive force to be generated betweenboth ends of the three-phase coil 131 or 141 and charges the HV battery194 (hereinafter this state of operation is referred to as the powergeneration or regenerative operation). Even when the switching elementsare not switched on, the rotation of the rotor in the motor causes themagnetic field formed by the permanent magnets to pass through thethree-phase coil. This varies the magnetic flux passing through thethree-phase coil and generates a counter electromotive force in eachphase coil. The counter electromotive force simply raises theinter-terminal voltage without any loading. When a load is connectedbetween the power lines L1 and L2, however, the electric current runsvia the protection diode D arranged in combination with each switchingelement. This enables the motor MG1 or the motor MG2 to carry out powergeneration. The power generation by utilizing the counter electromotiveforce will be discussed in detail later.

[0085] The HV battery 194 and the motors MG1 and MG2 are also connectedto an auxiliary machinery battery 198 via a converter 252. Thisarrangement enables the high voltage electrical energy generated by themotors MG1 and MG2 or accumulated in the HV battery 194 to be convertedinto a low voltage of DC 12[V] and charges the auxiliary machinerybattery 198 with the converted low voltage electrical energy.

[0086]FIG. 4A shows in detail the connection of the HV battery 194 withthe system main relay SMR. The HV battery 194 is divided into twobattery groups in the structure. The two battery groups are connectedwith each other via a high voltage fuse HF and a service plug SP. Theservice plug SP is provided to cut off the high voltage system forinspection, maintenance, and other purposes. Two system main relays SMR1and SMR2 are provided in the positive power line L1 of the HV battery194. The element actually included in the circuit is naturally thecontact of each relay. For convenience of explanation, here the contactis called the system main relay SMR. The system main relay SMR1 incombination with a current restriction resistor R for restricting theelectric current forms a bypass circuit, relative to the system mainrelay SMR2. A system main relays SMR3 is provided in the negative powerline L2 of the HV battery 194.

[0087] At the time of power supply of the high voltage system, the threesystem main relays SMR1, SMR2, and SMR3 are controlled according to thefollowing procedure. In order to start the operation of the vehicle, theprocedure first switches the system main relay SMR3 ON (in the closedstate) and then, after elapse of a preset time T1, the system main relaySMR1 ON. The system main relays SMR2 is switched ON after elapse ofanother preset time T2. When the system main relay SMR1 is closed asshown in FIG. 4B, the electric current starts flowing via the currentrestriction resistor R to restrict the magnitude of rush current. Thisarrangement effectively prevents the contact of the system main relaySMR1 from being welded by the arc of large electric current. Since theelectric current has already flown via the current restriction resistorR, the system main relay SMR2 in the closed state is protected fromwelding. At the time of cutting off the high voltage power source, asshown in FIG. 4B, the procedure first switches the system main relaySMR2 OFF (in the open state) and then, after elapse of a preset time T3,the system main relay SMR3 OFF. The system main relay SMR1 is switchedOFF after elapse of another preset time T4.

[0088] The system main relays SMR1, SMR2, and SMR3 are switched on andswitched off in different sequences at the time of power supply and atthe time of power cut off as described above. An HV battery sensor 196measures an output voltage Vbt of the HV battery 194, whereas a voltagesensor 197 measures a voltage Vhv of the power line. The welding failureof each system main relay SMR is detected according to the on-off stateof the system main relays SMR and the relation of the voltages Vbt andVhv. In the course of power supply, if Vbt=Vhv when the system mainrelay SMR3 is switched ON, the procedure determines that either thesystem main relay SMR1 or the system main relay SMR2 welds. In thecourse of power cut off, if Vbt=Vhv when the system main relay SMR1 isswitched OFF, the procedure determines that the system main relay SMR3welds. A diversity of methods are applicable to diagnose the weldingfailure. For example, one applicable method detects the welding failureby switching on and off the respective contacts in different sequences.Another method disposes a current sensor in a circuit passing througheach contact.

[0089] Referring back to FIG. 2, the power output system from the engine150 to the drive shaft is described. The rotating shafts of the engine150 and the motors MG1 and MG2 are mechanically linked with one anothervia a planetary gear 120. The planetary gear 120 includes a sun gear121, a ring gear 122, and a planetary carrier 124 with a planetarypinion gear l23. In the hybrid vehicle of the embodiment, the crankshaft156 of the engine 150 is coupled with a planetary carrier shaft 127 viaa damper 130. The damper 130 is provided to absorb torsional vibrationsarising on the crankshaft 156. The rotor 132 of the motor MG1 is linkedwith a sun gear shaft 125, whereas the rotor 142 of the motor MG2 islinked with a ring gear shaft 126. The rotation of the ring gear 122 istransmitted to an axle 112 and wheels 116R and 116L via a chain belt 129and a differential gear 114.

[0090] The control system 200 utilizes a diversity of sensors to attainthe control of the whole hybrid vehicle. Such sensors include anaccelerator sensor 165 that measures the amount of depression or step-onamount of an accelerator pedal by a driver, a gearshift position sensor167 that detects the position of a gearshift lever, a brake sensor 163that measures the step-on pressure of a brake pedal, a battery sensor196 that measures the charge level or state of charge (SOC) of the HVbattery 194, and a speed sensor 144 that measures the revolving speed ofthe motor MG2. The ring gear shaft 126 is mechanically linked with theaxle 112 via the chain belt 129, so that the ratio of the revolvingspeeds of the ring gear shaft 126 to the axle 112 is fixed. The speedsensor 144 disposed on the ring gear shaft 126 accordingly detects therevolving speed of the axle 112 as well as the revolving speed of themotor MG2.

[0091] B. Basic Operations in Hybrid Vehicle

[0092] The description first regards the operations of the planetarygear 120 to explain the basic operations in the hybrid vehicle. In theplanetary gear 120, when the revolving speeds of any two rotating shaftsamong the three rotating shafts mentioned above are specified, therevolving speed of the residual rotating shaft is automaticallydetermined. The revolving speeds of the respective rotating shafts holdthe relationship defined as Equation (1) given below:

Nc=Ns×ρ/(1+p)+Nr×1/(1+ρ)  (1)

[0093] where Nc, Ns, and Nr respectively denote the revolving speed ofthe planetary carrier shaft 127, the revolving speed of the sun gearshaft 125, and the revolving speed of the ring gear shaft 126, and ρrepresents the gear ratio of the sun gear 121 to the ring gear 122 asexpressed by the following equation:

ρ=[number of teeth of sun gear 121]/[number of teeth of ring gear 122]

[0094] The torques of the three rotating shafts hold fixed relationsdefined as Equations (2) and (3) given below, irrespective of theirrevolving speeds:

Ts=Tc×ρ/(1+ρ)  (2)

Tr=Tc×1/(1+ρ)=Ts/ρ  (3)

[0095] where Tc, Ts, and Tr respectively denote the torque of theplanetary carrier shaft 127, the torque of the sun gear shaft 125, andthe torque of the ring gear shaft 126.

[0096] The functions of the planetary gear 120 enable the hybrid vehicleof the embodiment to run in a variety of conditions. For example, in thestate of a drive at a relatively low speed immediately after the startof the hybrid vehicle, the motor MG2 carries out the power operation totransmit the power to the axle 112 and drive the hybrid vehicle, whilethe engine 150 is at a stop or at an idle.

[0097] When the speed of the hybrid vehicle reaches a predeterminedlevel, the control system 200 causes the motor MG1 to carry out thepower operation and motors and starts the engine 150 with the torqueoutput through the power operation of the motor MG1. At this moment, thereactive torque of the motor MG1 is output to the ring gear 122 via theplanetary gear 120.

[0098] When the engine 150 is driven to rotate the planetary carriershaft 127, the sun gear shaft 125 and the ring gear shaft 126 rotateunder the conditions fulfilling Equations (1) through (3) given above.The power generated by the rotation of the ring gear shaft 126 isdirectly transmitted to the wheels 116R and 116L. The power generated bythe rotation of the sun gear shaft 125 is, on the other hand,regenerated as electric power by the first motor MG1. The poweroperation of the second motor MG2 enables the power to be output to thewheels 116R and 116L via the ring gear shaft 126.

[0099] In the state of a stationary drive, the output of the engine 150is set substantially equal to a required power of the axle 112 (that is,the revolving speed×torque of the axle 112). In this state, part of theoutput of the engine 150 is transmitted directly to the axle 112 via thering gear shaft 126, while the residual power is regenerated as electricpower by the first motor MG1. The second motor MG2 utilizes theregenerated electric power to produce a torque for rotating the ringgear shaft 126. The axle 112 is accordingly driven at a desiredrevolving speed and a desired torque. The control operation of theengine 150 in the stationary driving state will be discussed later.

[0100] When there is an insufficiency of the torque transmitted to theaxle 112, the second motor MG2 supplements the insufficient torque. Theelectric power obtained by the regenerative operation of the first motorMG1 and the electric power accumulated in the HV battery 194 are usedfor such supplement. In this manner, the control system 200 controls theoperations of the two motors MG1 and MG2 according to the required powerto be output from the axle 112.

[0101] The hybrid vehicle of the embodiment may go back in the activestate of the engine 150. While the engine 150 is driven, the planetarycarrier shaft 127 rotates in the same direction as that in the case ofthe forward drive. In this state, when the first motor MG1 is controlledto rotate the sun gear shaft 125 at a higher revolving speed than therevolving speed of the planetary carrier shaft 127, the rotatingdirection of the ring gear shaft 126 is inverted to the direction forthe rearward drive as clearly understood from Equation (1) given above.The control system 200 makes the second motor MG2 rotated in thedirection for the rearward drive and regulates the output torque, thusenabling the hybrid vehicle to go back.

[0102] In the planetary gear 120, the planetary carrier 124 and the sungear 121 may be rotated while the ring gear 122 is at a stop. The engine150 is accordingly driven while the vehicle is at a stop. For example,when the HV battery 194 has a low charge level, the engine 150 is drivenand causes the first motor MG1 to carry out the regenerative operationand charge the HV battery 194. The power operation of the first motorMG1 in the stationary state of the vehicle, on the other hand, motorsand starts the engine 150 with the output torque.

[0103] C. Configuration of Control System in Embodiment

[0104]FIG. 5 is a block diagram illustrating the detailed configurationof the control system 200 in this embodiment. The master controller 270includes a master control CPU 272 and a power source control circuit274. The motor controller 260 includes a main motor control CPU 262 andtwo motor control CPUs 264 and 266 that respectively control the twomotors MG1 and MG2. Each of the CPUs is constructed as a one-chipmicrocomputer including a CPU, a ROM, a RAM, an input port, and anoutput port (not shown).

[0105] The master control CPU 272 functions to determine thecontrol-relating quantities, for example, the distribution of therevolving speeds and the torques of the three prime movers 150, MG1, andMG2 and transmit a diversity of required values to the other CPUs andECUs, so as to control the operations of the respective prime movers. Inorder to attain such control, accelerator position signals AP1 and AP2representing the accelerator position or opening, gearshift positionsignals SP1 and SP2 representing the gearshift position, and theignition signal IG that represents an ignition-related operation and istransmitted from the ignition sensor 169 are directly connected to aninput port of the master control CPU 272. The master control CPU 272also receives a brake signal BP transmitted from the brake sensor 163via the brake ECU 220. Both the accelerator sensor 165 and the gearshiftposition sensor 167 have a dual structure, that is, include two sensorelements. The master control CPU 272 accordingly receives the twoaccelerator position signals AP1 and AP2 and the two gearshift positionsignals SP1 and SP2. The master control CPU 272 also controls the on-offstate of the system main relays SMR to connect and cut off the highvoltage power source from the HV battery 194 as discussed above. For thepurpose of such on-off control, the master control CPU 272 monitors thestate of the ignition sensor 169 that detects a turning motion of anignition key. Indicators and lamps provided on an inner panel areconnected to an output port of the master control CPU 272. In theillustration of FIG. 5, only a diagnosis lamp 291 is shown as a typicalexample. The master control CPU 272 controls its output port to directlylight these indicators and lamps.

[0106] As illustrated in FIG. 5, the master control CPU 272 is connectedwith the converter 252 that converts the high voltage direct current ofthe HV battery 194 into low voltage direct current and with a voltagesensor 199 that is mounted on the auxiliary machinery battery 198 tomeasure the voltage of the auxiliary machinery battery 198 and output ameasurement signal VCE. The ignition sensor 169 outputs the startingrequirement signal IG in response to a turning motion of the ignitionkey. The starting requirement signal IG switches the relay 197 on toallow supply of the low voltage power source Vcc. The master control CPU272 receives the supply of the low voltage power source Vcc, switches onand off the system main relays SMR according to the voltage VCE of theauxiliary machinery battery 198, and controls the operations of theconverter 252 when required. The power source control circuit 274incorporated in the master controller 270 has the function of amonitoring circuit that monitors abnormality in the master control CPU272.

[0107] The main motor control CPU 262 transmits required electriccurrents I1req and I2req to the two motor control CPUs 264 and 266,based on required torques T1req and T2req of the two motors MG1 and MG2given by the master control CPU 272. The motor control CPUs 264 and 266respectively output the control signals Sw1 and Sw2 according to therequired electric currents I1req and I2req, so as to control the drivingcircuits 191 and 192 and drive the motors MG1 and MG2. The speed sensorsof the motors MG1 and MG2 feed revolving speeds REV1 and REV2 of themotors MG1 and MG2 back to the main motor control CPU 262. The mastercontrol CPU 272 receives the revolving speeds REV1 and REV2 of themotors MG1 and MG2 as well as a value of electric current IB suppliedfrom the HV battery 194 to the driving circuits 191 and 192, which arefed back from the main motor control CPU 262.

[0108] The battery ECU 230 monitors the state of charge or charge levelSOC of the HV battery 194 and supplies a required value of chargingCHreq of the HV battery 194, when required, to the master control CPU272. The master control CPU 272 determines the output of each primemover by taking into account the required value of charging CHreq. Inthe case of a requirement for charging, the master control CPU 272causes the engine 150 to output a greater power than the value requiredfor the drive and distributes part of the output power to the chargingoperation by means of the first motor MG1.

[0109] The brake ECU 220 carries out control to balance a hydraulicbrake (not shown) with the regenerative brake by the second motor MG2.This is because the second motor MG2 carries out the regenerativeoperation to charge the HV battery 194 in the course of braking thehybrid vehicle of the embodiment. In accordance with a concreteprocedure, the brake ECU 220 transmits a required regenerative powerREGreq to the master control CPU 272, based on the brake pressure BPmeasured by the brake sensor 163. The master control CPU 272 specifiesthe operations of the motors MG1 and MG2 in response to the requiredregenerative power REGreq and feeds an actual regenerative power REGpracback to the brake ECU 220. The brake ECU 220 regulates the amount ofbraking by the hydraulic brake to an adequate value, based on theobserved brake pressure BP and the difference between the requiredregenerative power REGreq and the actual regenerative power REGprac.

[0110] D. Control by Engine ECU

[0111] The engine ECU 240 controls the engine 150 according to thetarget revolving speed NE* transmitted from the master control CPU 272as discussed below. The engine ECU 240 basically carries out thefeedback control of the revolving speed. The master control CPU 272specifies the target revolving speed NE*. The engine ECU 240 obtains theactual revolving speed NE of the engine 150 and calculates thedifference ΔN between the actual revolving speed NE and the targetrevolving speed NE*. When the actual revolving speed NE is lower thanthe target revolving speed NE*, the engine ECU 240 controls the throttlemotor 152 to widen the opening θ of the throttle valve 151. The engineECU 240 also controls the air fuel ratio. When the throttle valve 151 isopen to increase the quantity of air intake, the quantity of fuelinjection τ increases accordingly. The procedure of feedback controlcarries out the PID control with a high gain G1 in a range ofsignificantly large difference ΔN between the actual revolving speed NEand the target revolving speed NE*. When the difference ΔN decreases tobe within a predetermined range ±E1, the control procedure changes thegain to a value G2 that is lower than G1. When the difference ΔN furtherdecreases to enter a very narrow range ±E2 (E2<E1), the controlprocedure varies the gain by a predetermined skipping value, in order tomake the revolving speed difference ΔN kept in this narrow range ±E2.Even in the control system where the response has a time lag of firstorder as in the case of the engine 150, this arrangement ensures thestability of control and makes the actual revolving speed coincidentwith the target revolving speed.

[0112] The throttle opening θ is anyway widened with an increase indifference ΔN. The hybrid vehicle of the embodiment regulates thedifference ΔN, so as to adjust the output (revolving speed×torque) fromthe engine 150. In order to enhance the output from the engine 150, thehybrid vehicle carries out the control to cause the difference ΔNbetween the target revolving speed NE* and the actual revolving speedNE. The control may raise the target revolving speed NE* or regulate therotational speeds of the motors MG1 and MG2 connected to each other viathe planetary gear 120 according to Equation (1) given above, so as toforcibly lower the revolving speed of the crankshaft 156.

[0113] Under the condition that the feedback control has caused theengine 150 to be driven at the target revolving speed NE* (thedifference ΔN=0), a decrease in reactive torque applied to thecrankshaft 156 immediately raises the revolving speed NE of the engine150. The decrease in reactive toque is caused, for example, bydecreasing the amount of depression AP of the accelerator pedal or bylowering the load of the drive shaft according to the configuration ofthe ground, for example, a change from an ascent to a descent. Theraised revolving speed NE causes the revolving speed difference ΔN. Theengine ECU 240 narrows the opening θ of the throttle valve 151 anddecreases the output of the engine 150, in order to cancel thedifference ΔN. When the revolving speed of the engine 150 is lowered bythe increased loading, on the contrary, there is also the revolvingspeed difference ΔN. The engine ECU 240 widens the opening θ of thethrottle valve 151 and immediately increases the output of the engine150, in order to cancel the difference ΔN. The output of the engine 150is also variable by varying the target revolving speed NE*.

[0114] As described above, while the engine ECU 240 feedback controlsthe revolving speed of the engine 150, the master controller 270 setsthe conditions to cause the revolving speed difference ΔN, so as toenable a desired power to be taken out of the engine 150. Even in thecase of an abrupt variation in loading, this control procedure does notrequire updating the target output given to the engine 150. The engineECU 240 transmits the actual revolving speed NE of the engine 150 to themaster control CPU 272, so that the master control CPU 272 is alwaysinformed of the actual revolving speed NE of the engine 150.

[0115] E. Other Configuration

[0116] As described above, the master control CPU 272 determines thetarget revolving speed of the engine 150 and the outputs of the motorsMG1 and MG2 and transmits the required values to the ECU 240 and theCPUs 264 and 266, which take in charge of the actual controls. The ECU240 and the CPUs 264 and 266 control the corresponding prime movers inresponse to the required values. The hybrid vehicle is accordinglydriven with the adequate power output from the axle 112 according to thedriving state. In the course of braking, the brake ECU 220 cooperateswith the master control CPU 272 to regulate the operations of therespective prime movers and the hydraulic brake. This arrangementattains the desirable braking operation that does not make the driveruneasy or uncomfortable, while allowing regeneration of electric power.

[0117] The two control CPUs 262 and 272 are connected to an abnormalityrecord registration circuit 280 via bidirectional communication lines214 and 216 to read and write data. There is another bidirectionalcommunication line 212 interposed between the master control CPU 272 andthe main motor control CPU 262 to transmit a variety of data includingverification of the validity of the processing.

[0118] An input port of the abnormality record registration circuit 280receives reset signals RES1 and RES2 transmitted between the mastercontrol CPU 272 and the main motor control CPU 262. The abnormalityrecord registration circuit 280 registers the input reset signals RES1and RES2 into an internal EEPROM 282. Namely the abnormality recordregistration circuit 280 has the function of monitoring generation ofthe reset signal and registering the generation record in response to areset of the master control CPU 272 or the main motor control CPU 262.

[0119] F. Control Procedure in Response to Detection of Failure

[0120] The following describes the control procedure carried out whenany abnormality arises in the HV battery 194 or the driving circuit 191.As described previously, when there is a failure in the HV battery 194or in the driving circuit 191 to interfere with the normal on-offoperation of the transistors Tr functioning as the switching elements,the control procedure sets the system main relay SMR OFF and enables thevehicle to be driven in the battery-less drive mode. In such cases, themotor MG1 functions as the generator utilizing the counter electromotiveforce. The failure of the HV battery 194 is identified, for example,when the state of charge or remaining charge SOC obtained from theobserved voltage by the HV battery sensor 196 is not varied by thecharging and discharging control via the driving circuit 191 or when anabnormal temperature level is detected by a temperature sensor (notsown). The failure of the switching elements in the driving circuit 191is identified, based on the measurements of the current sensors 181 and182.

[0121]FIG. 6 is a flowchart showing a failure detection-time controlroutine executed in the embodiment. This control routine is activated atthe time of detection of a failure and carried out after the system mainrelay SMR is set OFF. The system main relay SMR is set OFF at the timeof detection of the failure, since the power generation of the motor MG1by utilizing the counter electromotive force generally lowers theinter-power line voltage between the power lines L1 and L2 of thedriving circuit 191 below the inter-terminal voltage of the HV battery194. When the comparison between the inter-power line voltage and theinter-terminal voltage shows that the inter-terminal voltage of the HVbattery 194 is low, the control procedure may not set the system mainrelay SMR OFF.

[0122] When the program enters the control routine shown in theflowchart of FIG. 6, the procedure first reads the current vehicle speedSPD, the amount of depression AP of the accelerator pedal, and therevolving speed Nd of the drive shaft (that is, the axle) at step S100,and determines the target revolving speed NE* of the engine 150 based onthese inputs at step S110. The concrete process of step S110 reads thetarget revolving speed NE* of the engine 150 from a map provided forcontrol in the state of failure as shown in FIG. 7. In the map of FIG. 7used in this embodiment, the target revolving speed NE* of the engine150 increases with an increase in vehicle speed SPD. The solid curve ofFIG. 7 represents the base characteristic without taking into accountthe amount of depression AP of the accelerator pedal. In the actualstate, however, the target revolving speed NE* is varied according tothe amount of depression AP of the accelerator pedal. In a low vehiclespeed range, the target revolving speed NE* is raised with an increasein amount of depression AP of the accelerator pedal. This low vehiclespeed range is shown as a hatched area ORA in FIG. 7. In a concreteexample, when the driver depresses the accelerator pedal to the fullopen position, the target revolving speed NE* is set higher by 700 rpmthan the base value. When the accelerator pedal is depressed to the halfopen position, the target revolving speed NE* is set higher by 300 rpmthan the base value. The curve of broken line GD in FIG. 7 representsthe characteristic of the target revolving speed NE* under the conditionthat the accelerator pedal is depressed to the full open position.

[0123] Another procedure may set the engine speed NE* by taking intoaccount the differential of the depression amount AP of the acceleratorpedal. When the driver depresses the accelerator pedal, this procedureraises the target revolving speed NE* in advance while the vehicle speedSPD is still low. Namely this procedure raises the target revolvingspeed NE* to be higher than the level set in stationary state accordingto the map of the target revolving speed NE* against the vehicle speedSPB and the depression amount AP of the accelerator pedal. This methodeffectively ensures the future output of the engine 150 that will berequired in a short time period.

[0124] The revolving speed Nd of the axle or drive shaft, the revolvingspeed NE of the engine 150, and the revolving speed Ng of the motor MG1hold a relationship following Equation (1) given above. Namely there isthe relationship of:

NE=Ng×ρ/(1+ρ)+Nd×1/(1+ρ)  (1a)

[0125] The revolving speed Nd of the axle is obtained unequivocally fromthe vehicle speed SPD. Setting the revolving speed NE of the engine 150thus unequivocally determines the revolving speed Ng of the motor MG1.This relationship is shown in the map of FIG. 8. The three revolvingspeeds Nd, NE, and Ng always form a straight line (operation line OL).The revolving speed of the motor MG1 is thus adjusted by regulating therevolving speed NE of the engine 150. There is a time lag in the controlof the engine 150. Setting the target revolving speed NE* does notimmediately make the actual revolving speed of the motor MG1 coincidentwith the calculated revolving speed. The procedure then reads therevolving speed Ng of the motor MG1 at step S120.

[0126] In the arrangement of the embodiment, the revolving speed Ng ofthe motor MG1 functioning as the generator is varied according to thevehicle speed SPD and the depression amount AP of the accelerator pedal.This is because a maximum generated output Pgmx, which is taken out ofthe motor MG1 functioning as the generator by the power generationutilizing the counter electromotive force, depends upon the revolvingspeed Ng of the motor MG1. The procedure determines the maximumgenerated output Pgmx of the motor MG1 at step S130.

[0127] The process of determining the maximum generated output Pgmx isdescribed in detail. In the case of the power generation by utilizingthe counter electromotive force, as shown by the characteristic curvesof non-loading power generation NL and maximum power generation LD inFIG. 9, the voltage V of power generation increases with an increase inrevolving speed Ng of the motor MG1. The generated output P increaseswith an increase in revolving speed Ng as shown in FIG. 10. Under thecondition of a fixed revolving speed Ng, the voltage V of powergeneration decreases with an increase in generated output P as shown inFIG. 11. When the generated output P exceeds a predetermined value Pgmx,the voltage V abruptly decreases. The voltage V of power generationlower than a preset value does not allow the converter 252 to beactuated. The procedure of the embodiment thus sets the upper limit ofpower generation that ensures the voltage V of power generation to benot less than 150 V, as the maximum generated output Pgmx. The graph ofFIG. 11 shows the characteristic curve when the revolving speed Ng ofthe motor MG1 is equal to 6000 rpm. In this case, the maximum generatedoutput Pgmx is approximately equal to 4 kw.

[0128] The procedure inputs the revolving speed Ng of the motor MG1 atstep S120 and reads the maximum generated output Pgmx corresponding tothe input revolving speed Ng from the map stored in advance at stepS130. The procedure subsequently calculates a required torque Td of theaxle from the observed vehicle speed SPD and the depression amount AP ofthe accelerator pedal at step S140 and determines an output torque Tm ofthe motor MG2 to attain the required torque Td at step S150. Theprocedure then calculates an amount of power consumption Pm at step S160and regulates the output torque Tm to restrict the calculated amount ofpower consumption Pm to the maximum generated output Pgmx at step S170.The procedure subsequently controls the on-off state of the switchingelements or transistors Tr11 through Tr16 in the driving circuit 192 andcauses the motor MG2 to carryout the power operation with the torque Tmat step S180.

[0129] The power generation utilizing the counter electromotive forcedoes not carry out the on-off control of the transistors in the firstdriving circuit 191. As long as no load is connected between theterminals of the motor MG1, when the rotor with the permanent magnetsattached thereto rotates to vary the density of magnetic flux passingthrough the three-phase coil 131, the counter electromotive force isgenerated between the terminals to cancel the variation in density ofthe magnetic flux. As shown in FIG. 3, when the counter electromotiveforce is generated between the terminals of each phase coil in the motorMG1 and a load is connected between the power lines L1 and L2, theelectric current runs via the protection diode connected between thecollector and the emitter of each of the transistors Tr1 through Tr6.The magnitude of the electric current depends upon the magnitude of theloading. Namely the power generation utilizing the counter electromotiveforce automatically generates the electric power corresponding to theelectric power consumed by the loading within the range of the maximumgenerated output Pgmx. In the arrangement of the embodiment, themagnitude of the loading is adjusted by regulating the ON time of thetransistors Tr11 through Tr16 for the power operation of the MG2.

[0130] When there is any failure in the HV battery 194 or in the firstdriving circuit 191, the arrangement of the embodiment sets the systemmain relay SMR OFF and enables the vehicle to be driven in thebattery-less drive mode. In the battery-less drive mode, the engine 150is driven and the motor MG1 is used as the generator utilizing thecounter electromotive force. This ensures the power of severalkilowatts. In the case of the limp home drive in the state of failure,this arrangement ensures a certain level of vehicle speed and a drivingdistance determined by the remaining quantity of fuel (gasoline) in thevehicle. For example, when some abnormality arises in the vehicle duringa drive on an express way, this arrangement enables the vehicle to bedriven at the certain level of vehicle speed and thereby ensures thesafety of the drive.

[0131] The procedure of the embodiment varies the target revolving speedNE* of the engine 150 according to the required power of the vehicle andaccordingly regulates the revolving speed Ng of the motor MG1functioning as the generator, so as to adjust the maximum generatedoutput Pgmx in the power generation utilizing the counter electromotiveforce. This arrangement effectively prevents the engine 150 from beingcontinuously driven in a high speed range and overheated. The revolvingspeeds of the engine 150 and the motor MG1 vary according to the outputof the vehicle. This advantageously makes the driver feel compatibilityduring a drive of the vehicle.

[0132] The arrangement of the embodiment discussed above may besubjected to some modification. In the structure of the embodiment, theengine ECU 240 carries out the feedback control of the revolving speedof the engine 150, and the master control CPU 272 transmits the targetrevolving speed NE* to the engine ECU 240 through communication. In onemodified structure discussed below, there is no communication betweenthe master control CPU 272 and the engine ECU 240. In this example, theengine ECU 240 independently regulates the target revolving speed NE* ofthe engine 150. One example of the processing carried out in thismodified structure is shown in the flowcharts of FIGS. 12 and 14. Theflowchart of FIG. 12 shows a control routine executed by the mastercontrol CPU 272, and the flowchart of FIG. 14 shows a control routineexecuted by the engine ECU 240.

[0133] When the master control CPU 272 determines at step S200, based onthe driving conditions of the vehicle, that an increase in revolvingspeed of the engine 150 is required, the master control CPU 272increases the output torque Tm of the motor MG2 in a short time periodat step S210. This process increases the electric current flowingthrough the motor MG2 and thereby enhances the loading torque of themotor MG1 functioning as the generator. The loading torque is applied tothe engine 150, so that the revolving speed NE of the engine 150 istemporarily lowered at a timing tp1 shown in the graph of FIG. 13. Whenthe master control CPU 272 determines at step S200, based on the drivingconditions of the vehicle, that a decrease in revolving speed of theengine 150 is required, on the other hand, the master control CPU 272decreases the output torque Tm of the motor MG2 in a short time periodat step S220. This process decreases the electric current flowingthrough the motor MG2 and thereby reduces the loading torque of themotor MG1 functioning as the generator. The revolving speed NE of theengine 150 is thus temporarily heightened at a timing tp2 shown in thegraph of FIG. 13.

[0134] Referring to the flowchart of FIG. 14, the engine ECU 240continuously monitors the revolving speed of the engine 150 at stepS300. When the actual revolving speed NE of the engine 150 coincideswith the target revolving speed NE* at step S305, the engine ECU 240carries out the series of processing discussed below. The engine ECU 240compares a variation ΔNN in revolving speed NE per unit time with apredetermined range ±ΔNref at step S310. When ΔNN<−ΔNref, the engine ECU240 increments the target revolving speed NE* by a preset value N1 fromthe current level at step S320. When ΔNN>ΔNref, on the other hand, theengine ECU 240 decrements the target revolving speed NE* by the presetvalue N1 from the current level at step S330. In the case where thevariation ΔNN in revolving speed NE is within the predetermined range±ΔNref, the engine ECU 240 does not change the target revolving speedNE* of the engine 150 but keeps the current level.

[0135] While the master control CPU 272 and the engine ECU 240 do nottransmit data, the above control procedure enables the master controlCPU 272 to vary the revolving speed of the engine 150. In the structurethat allows communication between the master control CPU 272 and theengine ECU 240, even when there is a failure in the communicationsystem, this arrangement enables the revolving speed of the engine 150to approach a desired level and exerts the effects of the embodimentdiscussed above. This arrangement regulates the output of the engineaccording to the required torque of the vehicle and enables the vehicleto be driven with the required torque.

[0136] The above procedure regulates the target revolving speed NE* inresponse to a variation in actual revolving speed NE of the engine 150.In another modified arrangement, the engine ECU 240 directly detects thebehavior of the accelerator pedal, that is, the variation in depressionamount AP of the accelerator pedal (the operation in the openingdirection or the operation in the closing direction). The engine ECU 240regulates the target revolving speed NE* based on the detected behaviorof the accelerator pedal.

[0137] G. Battery-less Drive in Normal State of Inverters

[0138] The arrangement of the above embodiment causes the vehicle to bedriven in the battery-less drive mode in which the power generation iscarried out by utilizing the counter electromotive force on theassumption that there is a failure in the HV battery 194 or anotherrelated element. The vehicle may alternatively be driven in another typeof battery-less drive mode in which the power generation does notutilize the counter electromotive force but uses the driving circuits191 and 192 functioning as the inverters. The vehicle may be driven inthis type of battery-less drive mode in the normal state or in anabnormal state with a failure in the HV battery 194 while there is noabnormality in the driving circuits 191 and 192 functioning as theinverters. When there is an abnormality only in the HV battery 194, thebattery-less drive separating the HV battery 194 advantageously ensuresa drive of the high power performance. The battery-less drive stillexerts some advantages in the normal state where the HV battery 194 andthe driving circuits 191 and 192 are all normal. The drive of thevehicle in the state that the amount of power generation completelybalances with the amount of power consumption does not require eithercharging or discharging the HV battery 194, thus desirably extending thelife of the HV battery 194. In the case where the HV battery 194 has anexcessively high temperature through the charging or dischargingprocess, the battery-less drive with the HV battery 194 temporarilyseparated favorably gives the time of cooling does the HV battery 194.

[0139] In the case of the battery-less drive in the normal state, it isrequired to make the amount of power generation by the motor MG1 balancewith the amount of power consumption by the motor MG2. This is attainedby the series of processes discussed below:

[0140] (1) Calculation of required output of power generation Pgr: Theprocess specifies the current amount of power consumption by the motorMG2 including a loss of the system, so as to calculate a required outputof power generation Pgr, which represents the amount of electric powerto be generated by the motor MG1 functioning as the generator.

[0141] (2) Calculation of target torque Tgi: The process calculates atarget torque Tgi of the motor MG1 functioning as the generator as thesum of a base torque Tgb and a PI controlled value Tgf through voltagefeedback of the driving circuits 191 and 192.

[0142] (3) Calculation of maximum amount of power consumption Pmmx: Theprocess calculates a maximum amount of power consumption Pmmx by themotor MG2.

[0143] (4) Calculation of target torque Tm: The process calculates atarget torque Tm of the motor MG2, so as to make the amount of powergeneration by the motor MG1 balance with the amount of power consumptionby the motor MG2.

[0144] The battery-less drive in the normal state is described belowwith referring to the flowchart of FIG. 15. When the program enters thecontrol routine of FIG. 15, the procedure first reads the currentvehicle speed SPD, the amount of depression AP of the accelerator pedal,and the revolving speed Nd of the drive shaft (that is, the axle) atstep S400, and determines the target revolving speed NE* of the engine150 based on these inputs at step S410. The concrete process of stepS410 reads the target revolving speed NE* of the engine 150 from a mapprovided in advance. Here the map is different from the map for controlin the state of failure shown in FIG. 7 but is set according to thedriving efficiency of the engine 150.

[0145] The procedure then reads the values of the respective sensors toobtain the revolving speeds Ng and Nm of the motors MG1 and MG2 and thecurrent torque Tmi−1 of the motor MG2 at step S420. Here the subscript‘i−1’ represents the current observed value, and the subscript ‘i’represents the controlled value to be output.

[0146] The procedure then successively calculates the required output ofpower generation Pgr at step S430, the target torque Tgi of the motorMG1 from the base torque Tgb and the voltage feedback controlled torqueTgf at steps S440 and S450, the maximum amount of power consumption Pmmxat step S460, and the target torque Tm of the motor MG2 at step S470.The details of these processes are discussed below.

[0147] (1) Process of Calculating Required Output of Power GenerationPgr (Step S430)

[0148] The process first calculates energy Pm currently consumed by themotor MG2 from the revolving speed and the torque obtained at step S420according to Equation (11) given below:

Pm=(2π/60)×Nm×Tmi−1  (11)

[0149] The process then reads a current loss Pml of the motor system MG2corresponding to the revolving speed Nm and the current torque Tmi−1 ofthe motor MG2 from a loss map. The loss of the motor system increaseswith an increase in torque and with an increase in revolving speed. Oneexample of the loss map is shown in FIG. 16.

[0150] The process subsequently reads a current loss Pgl of thegenerator system corresponding to the revolving speed Ng and the currenttorque Tgi−1 of the motor MG1 functioning as the generator from asimilar loss map. The process then calculates the required output ofpower generation Pgr according to Equation (12) given below:

Pgr=−Pm−Pml−Pgl−Pdc  (12)

[0151] In Equation (12), Pdc denotes a loss of the converter 252.Although the loss Pdc can be regarded as a fixed value, for the enhancedaccuracy, the loss Pdc may be read corresponding to the voltages on thehigher side and the lower side and the consumed electric current on thelower side from a map. The above series of processing gives the requiredoutput of power generation Pgr according to Equation (12).

[0152] (2) Process of Calculating Target Torque Tgi of Generator (StepsS440 and S450)

[0153] The target torque Tgi of the motor MG1 functioning as thegenerator is obtained as the sum of the base torque Tgb and the voltagefeedback controlled torque Tgf as expressed:

Tgi←Tgb+Tgf  (13)

[0154] The base torque Tgb is obtained by simplified calculation ofEquation (14) given below, based on the fundamental relation ofenergy=revolving speed×torque:

Tgb=(60/2π)×Pgr/Ng  (14)

[0155] The base torque Tgb of the motor MG1 functioning as the generatoris namely obtained by dividing the required output of power generationPgr, which represents the amount of electric power to be generated bythe motor MG1, by the revolving speed Ng of the motor MG1. Theprocessing of step S440 calculates the base torque Tgb according toEquation (14).

[0156] The process subsequently calculates the voltage feedbackcontrolled torque Tgf. The calculation specifies the PI controlled valueTgf according to a difference ΔV between the observed voltage of powergeneration of the motor MG1 and a target voltage level. The motor MG1 issupposed to generate the required output of power generation Pgr, whichis calculated at step S430 and expected to be consumed by the motor MG2.The amount of power generation is thus supposed to balance the amount ofpower consumption. The loading of the motor MG2, however, abruptlychanges due to the varying road surface and other factors. Powergeneration of only the required output accordingly causes an excess oran insufficiency in generated output with a variation in loading. Thisleads to an abrupt change of the voltage between the power lines L1 andL2. The procedure accordingly measures the d.c. voltage of the powerlines and carries out feedback control to quickly compensate for thevoltage variation. The processing of step S450 adds the PI controlledvalue Tgf through the feedback of the d.c. voltage to the base torqueTgb, so as to specify the target torque Tgi of the motor MG1.

[0157] (3) Process of Calculating Maximum Amount of Power ConsumptionPmmx (Step S460)

[0158] The process first obtains a limit torque or maximum torque Tgmxof the motor MG1 functioning as the generator. The maximum torque isread from a torque map shown in FIG. 17. The torque Tg of the motor MG1is specified by the revolving speed Ng and the voltage Vm. In the caseof power generation via the driving circuit 191 functioning as theinverter, the torque Tg at a predetermined revolving speed Ng is reducedwith a decrease in voltage Vm. The maximum torque thus obtained may,however, not be fully taken out of the motor MG1. The torque of themotor MG1 functioning as the generator is the reactive torque againstthe torque of the engine 150 and can thus not exceed the output torqueof the engine 150. The maximum torque Tgmx read from the torque map ofFIG. 17 is accordingly restricted to a maximum torque Temx of the engine150. In the case where the maximum torque Temx of the engine 150 is lessthan the maximum torque Tgmx read from the torque map of FIG. 17, themaximum torque Temx of the engine 150 is set to the maximum torque Tgmxof the motor MG1. In the mechanical distribution type hybrid vehicle ofthe embodiment, the torque Tg of the motor MG1 and the torque Te of theengine 150 hold the following relation:

Tg=(1+ρ)×Te/ρ  (3a)

[0159] This corresponds to the case where Ts=Tg and Tc=Te in Equation(3). In this embodiment, Tg=Te/3.6.

[0160] Here the maximum torque Temx of the engine 150 is read from atorque map provided in advance. One example of the torque map is shownin FIG. 18. The maximum torque Temx of the engine 150 is set with regardto the revolving speed Ne and the cooling water temperature THW of theengine 150 as parameters. In the graph of FIG. 18, a solid curve WUrepresents the revolving speed-torque characteristic at the warm-up timeand a broken curve CS represents the revolving speed-torquecharacteristic at the cold time. Strictly speaking, the maximum torqueTemx of the engine 150 is affected by the altitude (that is, thedifference in air density) and the temperature of intake air. Theseparameters may be reflected on the maximum torque Temx in amulti-dimensional version of the torque map shown in FIG. 18. Themaximum torque Temx read from the torque map of FIG. 18 mayalternatively be corrected with the altitude and the temperature ofintake air.

[0161] After determining the maximum torque Tgmx of the motor MG1restricted to the maximum torque Temx of the engine 150, the processobtains a loss Pglmx under such output conditions (that is, therevolving speed Ng and the torque Tgmx). The loss Pglmx of the motor MG1is read corresponding to the revolving speed Ng and the maximum torqueTgmx from the loss map of FIG. 16 as in the case of the loss of themotor MG2. The process then calculates maximum generated energy Pgmx ofthe motor MG1 functioning as the generator from the maximum torque Tgmxand the revolving speed Ng according to Equation (15) given below:

Pgmx=(2π/60)×Ng×Tgmx  (15)

[0162] The current loss Pml of the motor system has already been readfrom the loss map of FIG. 16. The maximum energy Pmmx consumed by themotor MG2 is calculated from the maximum generated energy Pgmx of themotor MG1 functioning as the generator, the loss Pglmx of the motor MG1and the loss Pml of the motor MG2. The maximum energy Pmmx consumed bythe motor MG2 is accordingly equal to the remainder obtained bysubtracting the losses from the maximum generated output:

Pmmx=Maximum generated output−Losses

=−Pgmx−Pml−Pglmx−Pdc  (16)

[0163] Here the maximum generated output Pgmx of the motor MG1 has theminus sign. This is because the consumed energy is expressed as the plussign and the generated energy is expressed as the minus sign in theequations.

[0164] The energy balance is expressed as:

I×V=(Pm+Pml)+(Pg+Pgl)+Pdc  (17)

[0165] The first term on the right side represents the sum of theconsumed energy and the loss in the motor MG2, the second termrepresents the sum of the generated energy and the loss in the motorMG1, and the third term represents the loss of the converter 252. Whenit is assumed that all the generated electric power is consumed by themotor, I×V=0 in Equation (17). Namely Equation (17) is rewritten as:

Pm=−Pg−Pml−Pgl−Pdc  (18)

[0166] Whereas Equation (16) gives the maximum consumed energy under theconditions of the maximum torque and the maximum loss, Equation (18)gives the consumed energy at the time of stationary drive and isessentially equivalent to Equation (12).

[0167] (4) Process of Calculating Target Torque Tm of Motor MG2 (StepS470)

[0168] At the final stage in the series of the processing, the processdetermines a required torque Tmr of the motor MG2. The required torqueTmr is calculated by subtracting a direct torque (Te/p) from a requiredtorque Td of the axle as expressed:

Tmr=Td−Te/ρ  (19)

[0169] The required torque Td of the axle is read from a vehiclerequirement torque map shown in FIG. 19. This map gives the requiredtorque Td of the axle against the vehicle speed with regard to thedepression amount AP of the accelerator pedal (or the throttle openingθ) as a parameter. The direct torque is a specific portion of the torqueTe of the engine 150 transmitted to the axle and is defined as Te/ρaccording to Equation (5) given above.

[0170] The process then restricts the required torque Tmr of the motorMG2 thus obtained to an upper limit torque Tmmx. The upper limit torqueTmmx is calculated from the maximum consumed energy Pmmx of the motorMG2 specified by Equation (16) and the revolving speed Nm of the motorMG2 according to Equation (20) given below:

Tmmx=(60/2π)×Pmmx/Nm  (20)

[0171] The required torque Tmr of the motor MG2 determined by Equation(19) is compared with the upper limit torque Tmmx specified by Equation(20). The process restricts the required torque Tmr to the upper limittorque Tmmx and specifies the target torque Tm of the motor MG2 as:

Tm←Tmr(Tmr≦Tmmx)

Tm←Tmmx(Tmr>Tmmx)  (21)

[0172] Referring back to the flowchart of FIG. 15, the procedure outputsthe target torque Tm of the motor MG2 thus obtained at step S480. Thecontrol routine of FIG. 15 regulates the target torque Tgi of the motorMG1, which functions as the generator, based on the basic torque Tgb andthe voltage feedback controlled torque Tgf (step S450), and regulatesthe target torque Tm of the motor MG2 based on the maximum consumedenergy Pmmx of the motor MG2, which is obtained by subtracting thelosses from the maximum generated output according to Equation (16)(step S480). The revolving speed Ne of the engine 150 is under thefeedback control by the engine ECU 240. This arrangement makes theamount of power generation by the motor MG1 balance with the amount ofpower consumption by the motor MG2 and thus enables the vehicle to bedriven without charging or discharging the HV battery 194. The motor MG1functioning as the generator is subject to the feedback control with thecontrolled value Tgf based on the difference ΔV between the observedd.c. voltage of power generation and the target voltage. This feedbackcontrol ensures a quick response to the voltage variation andeffectively actualizes the battery-less drive, which has not beensufficiently attained by the simple balance of the power generation withthe power consumption.

[0173] H. Control Procedure in State of Weldinq Failure of System MainRelay

[0174] The following describes the control procedure in the state ofwelding failure of the system main relay SMR as an application of theembodiment. The cause of the welding failure of the system main relaysSMR1, SMR2, and SMR3 and the method of detecting the welding failurehave been discussed already. FIG. 20 is a flowchart showing a drivecontrol routine executed in the state of welding failure of the systemmain relay SMR. In the end of this drive control routine, the proceduredetects a welding failure of the system main relay SMR3 at the timingspecified in FIG. 4B at step S500 and registers the welding failure inthe abnormality record registration circuit 280 at step S510. When anext drive of the vehicle starts, the program enters this drive controlroutine of FIG. 20. The procedure first reads the contents of theabnormality record registration circuit 280 and determines whether ornot the system main relay SMR3 has a welding failure at step S600. Whenthere is a welding failure in the system main relay SMR3, the procedurelights the diagnosis lamp 291 on and successively closes the system mainrelays SMR1 and SMR2 to connect the HV battery 194 with the power linesL1 and L2 at step S610 as in the case of the control procedure in thenormal state. When there is no welding failure in the system main relaySMR3, on the other hand, the procedure carries out the drive control inthe normal state at step S680.

[0175] In the state of the welding failure, after closing the systemmain relays SMR1 and SMR2, the procedure activates the engine 150 atstep S620 as in the case of the control procedure in the normal state.Once the engine 150 is activated, the vehicle can be driven in thebattery-less drive mode as discussed in the above embodiment. Theprocedure accordingly waits until the driving state of the engine 150satisfies desired conditions at step S630. When the driving state of theengine 150 meets the desired conditions, the procedure opens the systemmain relays SMR1 and SMR2 to allow a shift to the battery-less drivemode at step S640. In either case, when the drive of the vehicle isterminated (steps S650 and S690), the procedure again detects thewelding failure of the system main relays SMR3 and registers the weldingfailure if detected (steps S500 and S510).

[0176] In the application of the embodiment described above, when awelding failure arises in the system main relay SMR3, the controlprocedure connects the HV battery 194 with the power lines L1 and L2 fora short time period until the engine 150 is activated. Once the engine150 is activated, the HV battery 194 is disconnected from the powerlines L1 and L2, and the vehicle is driven in the battery-less drivemode. In the case where the vehicle is involved in some trafficaccident, the vehicle stops to terminate the power generation and losethe voltage on the power lines L1 and L2. This protects the driver,mechanic, or any related people from electric shocks. In thebattery-less drive mode, the HV battery 194 is separated from the powerlines L1 and L2, so that the high voltage of the HV battery 194 is notapplied to the power lines L1 and L2.

[0177] I. Structure of Electrical Distribution Type

[0178] The above description regards the mechanical distribution-typeparallel hybrid vehicle that distributes the power of the engine 150 bymeans of the planetary gear 120. The technique of the present inventionis also applicable to the electrical distribution type hybrid vehiclethat uses a pair-rotor motor including a pair of rotors rotatablerelative to each other, in order to actualize a similar battery-lessdrive. FIG. 21 schematically illustrates the structure of a power outputsystem in the electrical distribution type hybrid vehicle. In this poweroutput system, one rotor of a clutch motor 330, which attains a variablesliding speed between two rotors, is connected to the crankshaft 156 ofthe engine 150. The other rotor of the clutch motor 330 is connected tothe drive shaft. An assist motor 340 is also linked with the driveshaft. In the electrical distribution type power output system, theclutch motor 330 and the assist motor 340 are driven via the invertercircuits as in the structure of the embodiment. The vehicle is driven inthe battery-less drive mode as in the case of the above embodiment, inwhich the on-off control of the inverter circuit connected to the clutchmotor 330 is terminated and the power generation utilizing the counterelectromotive force is carried out with electric current via theprotection diodes disposed in the inverter circuit.

[0179] J. Change of Drive Mode

[0180] The hybrid vehicle may be driven while changing the drive mode.FIG. 22 shows a change of the drive mode. The hybrid vehicle changes thedrive mode from a normal drive mode NDM without any failure orabnormality to a battery-less drive mode IBL using the first and thesecond driving circuits 191 and 192 constructed as the inverters, inresponse to detection of a failure in the HV battery 194 (on theassumption that the use of the first driving circuit 191 is allowed) orin response to detection of a welding failure in the system main relaySMR3. The battery-less drive mode IBL opens the system main relays SMR1and SMR2 to disconnect the HV battery 194 from the power line L1. In thecase of the welding failure in the system main relay SMR3, the procedurecloses the system main relays SMR1 and SMR2 and activates the engine150, prior to the shift to the battery-less drive mode IBL as describedin detail in ‘H. Control Procedure in State of Welding Failure of SystemMain Relay’. The details of the battery-less drive mode IBL using thefirst and the second driving circuits 191 and 192 functioning as theinverters are described in ‘G. Battery-less Drive in Normal State ofInverters’ and are thus not specifically described here.

[0181] The hybrid vehicle changes the drive mode from the battery-lessdrive mode IBL to a counter electromotive force power generation drivemode RVL when the first driving circuit 191 fails to prohibit furtherswitching operations, when the vehicle goes back in a range R in thestructure of the mechanical distribution type, or when some disturbancelowers the voltage under the control in the battery-less drive mode IBL.The details of the counter electromotive force power generation drivemode RVL are described in ‘F Control Procedure in Response to Detectionof Failure’. This drive mode RVL sets the target revolving speed NE* ofthe engine 150 according to the loading and causes the motor MG1 tocarry out power generation utilizing the counter electromotive force. Inthe case of the reverse drive in the range R in the structure of themechanical distribution type, the drive mode is shifted to the counterelectromotive force power generation drive mode RVL, in order to preventthe direct torque of the engine 150 from being inverse to and therebycanceling the driving torque of the drive shaft. The drop in voltage ofpower generation occurs in the case where the voltage feedback controlfails to recover the voltage level when a delay of the power generationcontrol against a disturbance or another factor abruptly lowers the d.c.voltage or when the significantly low temperature of the engine 150abruptly lowers its revolving speed. The voltage drop decreases theoutput torque (see FIG. 17), and the insufficient output torque does notallow recovery of the voltage level. In such cases, the drive mode isshifted to the counter electromotive force power generation drive modeRVL to stop the switching operations of the first driving circuit 191.This raises the inter-terminal voltage of the motor MG1 and causes powergeneration utilizing the counter electromotive force. When the voltageis recovered to a sufficient level for power generation via theswitching operations of the inverters, the drive mode is returned to thebattery-less drive mode IBL using the inverters. When there is a failurein the first driving circuit 191, the vehicle directly changes the drivemode from the normal drive mode NDM to the counter electromotive forcepower generation drive mode RVL.

[0182] The hybrid vehicle changes the drive mode from the counterelectromotive force power generation drive mode RVL to a battery drivemode BDM when the HV battery 194 has a sufficient high voltage as itsstate of charge SOC. In the battery drive mode BDM, the first drivingcircuit 191 is not usable while the use of the second driving circuit192 is allowed, so that the vehicle is driven as the electric vehicle.At the time of stopping the vehicle driven in this battery drive modeBDM, the motor MG2 carries out the regenerative operation to regeneratethe electric current and charges the HV battery 194 via the seconddriving circuit 192. This recovers the state of charge SOC of the HVbattery 194. When the voltage of the HV battery 194 gradually decreasesto or below a specific level, at which the HV battery 194 can notactuate the converter 252 (approximately 140 volts in the embodiment),the drive mode is returned to the counter electromotive force powergeneration drive mode RVL. In the battery drive mode BDM, a brakingoperation ensures a braking force corresponding to engine brake andbesides enables the braking energy to be regenerated as electric power.

[0183] When engine brake is required in the course of deceleration orwhen the vehicle fails to climb a steep ascent and goes back, thevehicle changes the drive mode from the battery-less drive mode IBLusing the inverters to a motoring drive mode EBM. In the course ofdeceleration, the motoring drive mode EBM cuts off the supply of fuel tostop combustion of the fuel in the engine 150 and uses the motor MG2 asthe generator to regenerate the braking energy in the form of electricpower. The regenerated energy is consumed by the power operation of themotor MG1 to motor the engine 150. When the vehicle goes backunintentionally on a steep ascent, the axle rotates reversely and themotor MG2 functions as the generator. It is thus required to cancel therestriction of the torque, which is calculated from the power of themotor MG1 supposed to function as the generator, to the upper limittorque Tmmx. In such cases, the electric power generated by the motorMG2 is also consumed by the power operation of the motor MG1 to motorthe engine 150.

[0184] When the vehicle speed is reduced to decrease the consumableenergy for motoring and the regenerative electric power becomes greaterthan the consumed electric power for motoring, the vehicle changes thedrive mode from the motoring drive mode EBM to a zero torque drive modeTZM where the target torque Tm of the motor MG2 is set equal to zero. Inthe zero torque drive mode TZM, the vehicle is subject to noregeneration of electric power nor motoring.

[0185] The hybrid vehicle is driven while changing the drive mode in theabove manner. Among the various drive modes, the normal drive mode NDMhas the greatest output. The battery-less drive mode IBL using theinverters has the greater output than the counter electromotive forcepower generation drive mode RVL. It is not necessary to adopt all thedrive modes shown in FIG. 22. Any combination of required drive modesmay be applied according to the design and other requirements of thevehicle. Another possible modification provides a greater number ofdrive modes and changes the drive mode at a greater number of stagesaccording to the requirements.

[0186] The above description regards the application of the presentinvention, some embodiments according to the present invention, andcontrol procedure of changing the drive mode. The above description is,however, to be considered in all aspects as illustrative and notrestrictive. There may be many modifications, changes, and alterationswithout departing from the scope or spirit of the main characteristicsof the present invention. All changes within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

[0187] The scope and spirit of the present invention are indicated bythe appended claims, rather than by the foregoing description.

What is claimed is:
 1. A hybrid vehicle with an engine, a generator, anda motor mounted thereon, said engine outputting power through combustionof a fuel, said generator provided with permanent magnets generatingelectric power with at least part of the power output from said engine,said motor outputting power to a drive shaft of said hybrid vehicle,said hybrid vehicle comprising: an engine control unit that feedbackcontrols a quantity of the fuel injected to said engine to attain aspecified target if revolving speed of said engine; a power generationcontrol unit that causes said generator to carry out power generationutilizing a counter electromotive force; a loading detection unit thatspecifies a loading applied to said hybrid vehicle; a generatorrotational speed variation unit that varies a rotational speed of saidgenerator, based on the specified loading; and a motor driving unit thatdrives said motor with the electric power generated by said generator atthe varying rotational speed.
 2. A hybrid vehicle in accordance withclaim 1 , said hybrid vehicle comprising: an inverter that switcheselectric current running through a multiphase coil of said generator; asecondary battery that is charged with the direct current converted bythe switching operation of said inverter: an abnormal state detectionunit that detects an abnormal state, which does not allow said secondarybattery to be charged via said inverter; and an abnormal-state controlunit that carries out a specific control, which causes said powergeneration control unit, said generator rotational speed variation unit,and said motor driving unit to implement their functions, in response todetection of the abnormal state by said abnormal state detection unit.3. A hybrid vehicle in accordance with claim 2 , said hybrid vehiclefurther comprising: an operation unit that prohibits the powergeneration utilizing the counter electromotive force via said powergeneration control unit but drives said motor with electric poweraccumulated in said secondary battery, when an observed voltage level ofsaid secondary battery is higher than the counter electromotive forceutilized for the power generation via said power generation controlunit.
 4. A hybrid vehicle in accordance with claim 1 , said hybridvehicle further comprising: a target revolving speed setting unit thatspecifies the target revolving speed of said engine transmitted to saidengine control unit, based on behavior of an accelerator pedal.
 5. Ahybrid vehicle in accordance with claim 1 , wherein said generatorrotational speed variation unit increases the rotational speed of saidgenerator with an increase in amount of depression of an acceleratorpedal.
 6. A hybrid vehicle in accordance with claim 1 , wherein saidgenerator rotational speed variation unit lowers or raises the targetrevolving speed of said engine in response to detection of an increasingtendency or a decreasing tendency of an actual revolving speed of saidengine relative to the target revolving speed of said engine transmittedto said engine control unit.
 7. A hybrid vehicle in accordance withclaim 2 , wherein said abnormal state detection unit detects theabnormal state and activates said abnormal-state control unit to carryout the specific control, when an external force makes the drive shaftinversely rotated and said motor fall into a state of power generation.8. A hybrid vehicle in accordance with claim 1 , wherein said motordriving unit comprises: a maximum electric power setting unit that setsa maximum electric power generated by said generator with the power ofsaid engine; a driving electric power computation unit that specifiesdriving electric power consumed for driving said motor within the presetmaximum electric power, based on the specified loading; a powergeneration unit that causes said generator to generate electric powerthat is equivalent to the driving electric power consumed by said motor;and a current regulation unit that regulates electric current runningthrough a multiphase coil of said motor with the generated electricpower.
 9. A hybrid vehicle with an engine, a generator, and a motormounted thereon, said engine outputting power through combustion of afuel, said generator generating electric power with at least part of thepower output from said engine, said motor outputting power to a driveshaft of said hybrid vehicle, said hybrid vehicle comprising: an enginecontrol unit that feedback controls a quantity of the fuel injected tosaid engine to attain a specified target revolving speed of said engine;a generative energy computation unit that computes an instantaneousmagnitude of generative energy to be generated by said generator bytaking into account an energy balance in a system including said engine,said generator, and said motor; a voltage measurement unit that measuresa generative voltage of said generator; a control variable computationunit that computes a feedback control variable corresponding to adifference between the observed generative voltage and a targetgenerative voltage of said generator; a generator control unit thatfeedback controls said generator with the calculated instantaneousmagnitude of generative energy and the calculated feedback controlvariable; a requirement detection unit that detects a requirement on adrive of said vehicle; and a motor driving unit that calculates anoutput torque of said motor based on a direct torque output from saidgenerator, which is under control of said generator control unit, and arequired torque related to the detected requirement on the drive of saidvehicle, and drives said motor to attain the calculated output torque.10. A hybrid vehicle in accordance with claim 9 , said hybrid vehiclefurther comprising: an inverter that switches electric current runningthrough a multiphase coil of said generator; a secondary battery that ischarged with the direct current converted by the switching operation ofsaid inverter; and a state-of-failure detection unit that detects astate of failure in feedback control of said generator using thefeedback control variable, wherein said generator uses permanent magnetsto form a magnetic field, and said generator control unit comprises amechanism that stops the switching operation of said inverter and causessaid generator to carry out power generation utilizing a counterelectromotive force, in response to detection of the state of failure infeedback control of said generator.
 11. A hybrid vehicle in accordancewith claim 9 , said hybrid vehicle further comprising: a motoring unitthat, in a specific driving state where said motor generates electricpower, stops the fuel injection to said engine and causes said generatorto motor said engine and thereby consume the electric power generated bysaid motor.
 12. A hybrid vehicle with an engine, a generator, and amotor mounted thereon, said engine outputting power through combustionof a fuel, said generator generating electric power with at least partof the power output from said engine, said motor outputting power to adrive shaft of said hybrid vehicle, said hybrid vehicle comprising: anengine control unit that feedback controls a quantity of the fuelinjected to said engine to attain a specified target revolving speed ofsaid engine; a secondary battery that is connectable with both positiveand negative power lines of a direct voltage source, which link saidgenerator with said motor; a first contact that switches on and of fconnection of said secondary battery with one of the two power lines andlinks said secondary battery with the power line via a restrictionresistor, which restricts electric current flowing out of said secondarybattery; a second contact that is connected to the first contact inparallel and directly links said secondary battery with the power line;a third contact that switches on and off connection of said secondarybattery with the other of the two power lines; a weld detection unitthat detects a weld of the third contact; and a welding-state drivingunit that opens both the first contact and the second contact afteractivation of said engine in response to detection of the weld of thethird contact, and drives said motor with the electric power generatedby said generator.
 13. A hybrid vehicle in accordance with claim 12 ,said hybrid vehicle further comprising: a voltage measurement unit thatmeasures both an inter-terminal voltage between terminals of saidsecondary battery and an inter-power line voltage between the two powerlines; a decision unit that compares the observed inter-terminal voltagewith the observed inter-power line voltage while said welding-statedriving unit drives said motor; and a welding-state drive stop unit thatstops a drive of said vehicle when said decision unit determines thatthe observed inter-terminal voltage is equal to the observed inter-powerline voltage.
 14. A hybrid vehicle in accordance with any one of claims1, 9, and 12, wherein said generator has a pair-rotor structureincluding a pair of mutually rotatable rotors and carries out powergeneration to attain a voltage and electric power corresponding to asliding rotational speed of the two rotors.
 15. A hybrid vehicle inaccordance with any one of claims 1, 9, and 12, wherein said generatoris linked with one shaft of a three-shaft power distributor, in whichpower input to and output from one shaft is determined when powers inputto and output from residual two shafts are specified, and another shaftof said three-shaft power distributor is linked with an output shaft ofsaid engine and still another shaft of said three-shaft powerdistributor is linked with the drive shaft of said vehicle.
 16. A hybridvehicle in accordance with any one of claims 1, 9, and 1, wherein saidgenerator is connected to a first electric power driving circuit thatcauses said generator to carry out either one of a generative operationand a power operation based on an on-off state of switching elementsincluded in said first electric power driving circuit, said motor isconnected to a second electric power driving circuit that causes saidmotor to carry out either one of a power operation and a generativeoperation based on an on-off state of switching elements included insaid second electric power driving circuit, and said first electricpower driving circuit is connected to said second electric power drivingcircuit.
 17. A hybrid vehicle in accordance with claim 16 , said hybridvehicle further comprising: a cutoff unit that cuts off connectionbetween said secondary battery and said first electric power drivingcircuit; and a cutoff control unit that actuates said cutoff unit to cutoff the connection between said secondary battery and said firstelectric power driving circuit, when a generative voltage by saidgenerator is higher than an inter-terminal voltage between terminals ofsaid secondary battery.
 18. A method of controlling a hybrid vehicle,wherein an engine outputs power through combustion of a fuel, agenerator provided with permanent magnets generate electric power withat least part of the power output from said engine, and a motor isdriven with at least part of the electric power generated by saidgenerator, so as to output power to a drive shaft of said vehicle, saidmethod comprising the steps of: feedback controlling a quantity of thefuel injected to said engine to attain a specified target revolvingspeed of said engine; causing said generator to carry out powergeneration utilizing a counter electromotive force; specifying a loadingapplied to said hybrid vehicle; varying a rotational speed of saidgenerator, based on the specified loading; and driving said motor withthe electric power generated by said generator at the varying rotationalspeed.
 19. A method of controlling a hybrid vehicle, wherein an engineoutputs power through combustion of a fuel, a generator provided withpermanent magnets generate electric power with at least part of thepower output from said engine, and a motor is driven with at least partof the electric power generated by said generator, so as to output powerto a drive shaft of said vehicle, said method comprising the steps of:feedback controlling a quantity of the fuel injected to said engine toattain a specified target revolving speed of said engine; computing aninstantaneous magnitude of generative energy to be generated by saidgenerator by taking into account an energy balance in a system includingsaid engine, said generator, and said motor; measuring a generativevoltage of said generator; computing a feedback control variablecorresponding to a difference between the observed generative voltageand a target generative voltage of said generator; feedback controllingsaid generator with the calculated instantaneous magnitude of generativeenergy and the calculated feedback control variable; detecting arequirement on a drive of said vehicle; and calculating an output torqueof said motor based on a direct torque output from said generator, whichis under control of said generator control unit, and a required torquerelated to the detected requirement on the drive of said vehicle, anddriving said motor to attain the calculated output torque.
 20. A methodof controlling a hybrid vehicle, wherein an engine outputs power throughcombustion of a fuel, a generator provided with permanent magnetsgenerate electric power with at least part of the power output from saidengine, and a motor is driven with at least part of the electric powergenerated by said generator, so as to output power to a drive shaft ofsaid vehicle, said method comprising the steps of: connecting asecondary battery with both positive and negative power lines of adirect voltage source, which link said generator with said motor;interposing a first contact between said secondary battery and one ofthe two power lines via a restriction resistor, which restricts electriccurrent flowing out of said secondary battery; connecting a secondcontact to the first contact in parallel, the second contact directlylinking said secondary battery with the power line; interposing a thirdcontact between said secondary battery and the other of the two powerlines; feedback controlling a quantity of the fuel injected to saidengine to attain a specified target revolving speed of said engine;detecting a weld of the third contact; and opening both the firstcontact and the second contact after activation of said engine inresponse to detection of the weld of the third contact, and driving saidmotor with the electric power generated by said generator.